Negotiating should always be based on your budget, not her "worth." Her "worth" is a subjective, ambiguous amount. How much is she "worth" at any given time? She is priceless! Just ask her (because her opinion is all you have)?  

 
On the other hand, your budget is an objective, measurable amount. It's your actual budget, and she can't really argue that.  

 
I am assuming you just don't want to go with $800 with same frequency (# BCD's/month) as other SB's.  

 
So first, you can try the money over time model:  
If your budget is $500 3x a month, that's $1,500 a month assuming you consistently meet your schedule.  So if you don't think she will come down from $800, then stretch the proposed schedule to 2x a month for a total of $1,600 or meet once every 3 weeks for an average of $1,200 a month over a 3-month period.  This works best with SB's who are all about the money (vs. luxury lifestyle). It works even better for SB's that are, or will be, dating multiple SD's, as she will fill up the downtime with other old, wrinkled penises.  

 
Next, you can try the value vs price model:  
Tell her this: "If we can agree on $500 per meeting, I will be able to provide more exceptional experiences for us. We can go to more nice restaurants, travel more often, I can buy you better gifts, etc."  This works best with SB's who are equally interested in all the upscale lifestyle events you can provide as well as, or more than, the money.  

 
Bottom line: Do not offer $1 more than you are comfortable offering. That will eventually erode any satisfaction you will get from this arrangement. Neither of the 2 models above are perfect, but they should serve as a guideline to get you closer to your goal of enjoying that sweet, box-checking pussy.  

 
Life is good

 
The Cat

I would never negotiate with a provider. If her price is above my means, I say thank you and tell her to have a good day. First off, most providers will not negotiate their price down so it's rather pointless. Some might even block you and bad mouth you to their friends. If she actually accepts your lower than her asking price offer, she might not come with the same energy you want. At that point, she is likely not happy that you are paying less than she wants and, therefore, you may not get the service you want. Of course, if this happens, you can just move on. I am risk adverse, so I prefer not to take this chance. But if you're a gambling man and really want to see her and spend less, you can see what happens. Just know the risk.

As usual, great words of wisdom I will second.
I would add this: Think about what you see as her motivation in this. There are some gals who are not interested in us guys but will lay themseves down if the price is right. These tend not to be the best arrangements, from my view. There are others who want  a guy they can cnnect with and have fun with, and the cash is gravy on top. These tend to be better for me -- although you have to make your own choices. If it's the latter I would try to make it work as Herb suggested. Logically, if she is looking for $1600 a month that would mean roughly 3 meetings a month instead of two. If the meetings are fun for both parties. it's a win-win. But if this gal wants to pull own $800 every week she may be dreaming or out of your league.

Remind her, you want to see her often and consistently, 800 isn't in the cards for that.  Does she want a 1-2 time 800 or a consistent 1500-2000 per month?  If she only wants the 800 she's more likely to drop you the second she gets more from someone or just be seeing tons of guys, if you are ok with that then sure.  I like arrangements more exclusive, can go without condoms.  No chance of catching anything.

I have never paid more than  500 ppm in LA and even some girls who initially start w 600-700 once they meet me in person and we get along, don’t mind 500 at all  

800 is a bit high -you may be able to bring her down to 600 if she liked you but if she is firm at 800, don’t bother unless you can put up 800 consistently . Otherwise the sex will be mediocre  

Frankly speaking -  early on when I was a newbie —  I once negotiated a 1000 girl to 750 and had sex w her at a 300 dollar hotel - incl parking etc that was 1100 dollars down the drain and I learned my lesson - never to do that again  

More money does not equal better experiences

Met POT SB at a wine bar.  She's clearly looking to improve her life's experiences more so than "lifestyle".  Her goals are to travel, learn to ski, play golf, become knowledgeable about wine, paint, etc...  All of these (except painting) are in my wheelhouse.  After the M&G she texted wanting to coordinate schedules for next week.

Will take her to a nice dinner spot, have great wine and conversation.  I'm going to stick with my original offer of $500 for 2-3 meets/mont.  In reality, it will be 1-2/month as she's joining the rotation, but 2-3 sounds better to most SB's.  In my experience, once you treat them well, have a great time, don't get possessive/intrusive, the frequency becomes less important. Can do $600 if she hosts, and will walk if she doesn't accept my offer.  

What others have said is absolutely great advice.
My only contrarian comment is this:
The actual "worth" of a girl depends mostly on her 'hotness'
From 1-10, multiply by 100 to get an expected ppm
Of course, if you are younger and good looking a minus of -20% is reasonable.  
Basically, the HOT ones charge up to 1K - it's up to you if it's worth it.
These days, you better have an income of 200-400K to play, otherwise expect someone like me to beat you to the prize.
...and you know we are all brothers here, so comments offered are in the spirit of that.