I like leaving the envelope in the bathroom when I first get there like you said. The lady usually freshens up in there after I do, so it's there if she decides to check it. To me, this seems to be the best way to handle things. It's discreet, professional, and puts her at ease.

Regarding your website changes, the code that makes up your site is pretty straight forward. It wasn't generated with some exotic web-design tool, so the code is easy to read and change. It won't take someone with "mad skillz" to update it for you. Some entry-level to intermediately skilled person is bound to be able to help you.

it is understood

that all monies being exchanged occur afterwards. Any deviation from this practice alerts me that there is the potentiality for le, and s/he is quickly escorted to the door. I tell this to the clients at my preliminary screening prior to booking, and just as a testament to this practice, I have had a couple of cancellations with no rescheduling...and true to form, they get a Krispy Kreme coupon in their e-mail. Le seems to not complain.

Provided of course that she tells me her preference.  Otherwise I'll leave an envelope on the nightstand, dresser, whatever fits the setup at the beginning.  At the end I'll sometimes even ask her to count it.  Hey, I have been known to make a mistake once or twice.

Under the TV remote EOM.

Have you thought of redoing the entire thing?
I did and I am very happy with the end results.
My webguy is very talented.
Check out my link attached.
Best Wishes!
V~