A top notch and wonderful provider recently sent me a message stating she would be visiting my city and would love to see me next month.  The truth is I would really like too, however I am having some cash flow issues, it's the end of year, etc.  How can I tell her tactfully that is really tough to meet her expectations.  I never negotiate nor ever ask for favors outside anyone rates.  I understand this is a business, but saying no is never easy, or rather saying not right now.

1)  Go the direct and honest route:  Tell the truth that you're having financial difficulty and can't afford her donation at the moment even though you really wanted wanted to see her. Tell her hopefully the next time she comes by you maybe in better financial shape.  

If it were me, I would respond with a polite email: "would love to see you, but cannot at this time due to special circumstances. Look forward to getting together on the next visit".

.its a business transaction. Once you realize that your problem is solved.

Don't put too much information. Like someone said she is not the only recipient of the email (likely has an assistant or some such). Say you cant make it, cite 'special circumstances' or 'a lot going on in my life right now'.

You can say unfortunately you will not be able to see her on this visit you have some things you need to handle.But to let you know when she returns hopefully you can see her the next time.
I think you are overthinking this a bit.I am sure she will understand.

You don't want to seem like you're looking for a discount, but you don't want her to ignore you for future dates if you tell her you can't afford her this time. So don't explain. Just say you can't this time, but hope she will keep you in mind in the future. Good enough.

you're under no obligation, then give her my contact info, I'm on a new quest

She is a professional sex worker---not your GF or wife. You are under absolutely no obligation to 'meet her expectations'.  

Nothing wrong with just politely saying "current financial situation won't allow but would love to see you on next trip."

Who doesn't have from time to time financial woes. Tell her I'm sorry I can't see you due to financial issues. Hopefully we will see eachother soon. The End.

" save face for both of us "

Everyone has had cash flow issues in the past, well almost everyone anyway. She will understand.

And don't banter back and forth via email until you have the money and book a date. This is not said in any heart, but to tell you what will drive many ladies nuts.

Tell her that you have been recruited by the CIA to go to Syria and find the head of ISIS and chop his head off, so it's a bad time for you, but feel free to contact you in the future.

She read your post.

It's so shocking you know they're lying, but funny as hell so you just let them lie. LOL

depending of course on who initiated this announcement. If he PM'd her asking her to come to town he of course owes her a reply and an explanation, if on the other hand she simply sent out a blanket email to several dozen potential customers, the kind of PM's/Emails I get all the time, he doesn't even owe her a reply, much less an explanation.

he is looking for head?  How would that help?  It might seem like he is booked with another traveler and her feelings get hurt.

We have people like that here ... I think it's called, "Schizophrenia"

I'm sorry, but did you just call me a "ho"?

he doesn't owe her anything.

The business savvy providers will continue to contact you even when you have said no more than once, as they know how to keep track of past clients. They know that there is a time when business may be sparse, so it will always be good to get the word out to past satisfied customers.  

that way it does not seem that you are bargaining. Then be honest. Nothing wrong with it,  
And she knows you, so one can see who has a shady character and who is genuine.