I've never had problems getting a 2 hour session at most MP's. I only do 2 hours with my top favourite MPA's ( only 2 have reached that status - infatuation ) 'cause anything less just leaves me wanting more and doesn't seem like enough time. It's not like I can afford it and my visa will verify that ( overdraft ), but I'd rather have one full experience than two lesser ones.
The price quoted by Punkdt is over the top, in my experince. You just have to juggle your options a bit*. Depending on the MPA and / or your rapport with her they may set a special flat rate seeing as it's a longer session, but don't quote me on that. ( BBG status ) It's not about being "cheap", but I think more about what is a "fair" price.
Time is precious
Of course if you expect "top tip" fun throughout the entire two hours then you should also be prepared to pay for it.
Believe me, if I had a disposable income I'd be booking an entire shift at a time at whatever rates their little hearts desire, but at infrequent intervals so others get a chance and it just keeps things more "alive" overall.