Expensive visit coming up. Should the donation be in large bills (easier to count) or small bills (hard to count, but easier to use afterwards?)

Short answer = any legal tender is fine.

Longer answer - if her fee is several hundred dollars, the less bills the better for a quick confirmation that it's correct.  I always use 100's, and only one time did the lady mention the need to get change to tip the valet.  I happen to live in a large metropolitan area that is very cash driven.  If you're seeing a girl in Backwoods, USA, consider giving her the last hundred in small bills.

I have found that prices seem to move in even $50 steps and it is handy to buy up-sell services in "round" $50 increases as well...
All though, For "erotic massage" or AMP hobbying, I find that $20's are better, since the service menu moves in smaller steps in these sub-markets, I find it more handy for up-sell negotiating and tipping to NOT have any large bills in my pocket!  (IMHO)

You're finished up in under 10 minutes (after that I start to jones)
If you give me a few minutes "alone" in the bathroom, I'll come back and give you a BBBJ-TC-CIM for the second $20.
(again, as long as you can finish up in under 10 minutes!)
For another $20, (after "Mr. Jones" goes away again that is) I'll rim ya while probing the brown eye, and share it with you in a DFK if you'd like!
 Anything after that, is free, 'cuz after the third hit, I pass out...

Although frugal I was hoping for something  insalubrious for my money.

THREE HITS and you're OUT?.....Light weight!

I just said that anything AFTER 3 is free! 'Cuz I ain't awake anymore to charge you! If you want some BBFS followed by some DATY, then help yourself!

Crack is an adulterated form of Cocain. After three good hits and a final "push" on the pipe you should be awake enough to paint my entire house; trim & all let alone be awake while I blast your bunger.

For the advanced crack user, the sudden drop on blood-pressure after the first few hits when the heart goes into "flutter" usually leaves them sleepy or completely out,,, until Mr. Jones wakes them up that is...  But Meth on the other hand, that seems to keep 'em going like the energizer bunny for days straight!

a community of lechers and mercenarys

inless than 100 years! These same "drugs" were used in different forms by many social elites only a century ago "Cocaine" and "amphetamine" were comonly prescribes "tonics" in the by-gone era... It just further proves the effects of "criminalizing" any personal choice! And in that we do share a tie....