There isnt alot of touch screen phones on a prepaid service, but i do know some. (:
LG Rumor Touch-Virgin Mobile- $119.99(at Target) $149.99 at other stores.
Its a pretty good looking phone slides out into a qwerty keyboard and great plans!
The best one i think is the $25/month for UNLIMITED text, web, email, and data. WITH 300 mins.
You can watch youtube videos on it! And its also has a music player!
T-Mobile Tap- $120
This phone is new so i dont know much about it, but i HEARD it sucks. Then again, you never know until you try it out
Straight Talk Finesse Prepaid Touch Screen Cell Phone-Price varies.
http://www.walmart.com/ip/Straight-Talk-...
Motorola i1-Boost Mobile-$349.99
This comes with a plan of $50 a month for UNLIMITED talk, text, web, im , email, push to talk, etc.
I know its over the budget but it really seems like a good phone to me.
LG Prime (TM)-Go Phone for AT&T- 99.99
They say its an alright phone, its a basic touchscreen phone.
AND!
You can always buy the FULL RETAIL PRICE for a any phone on verizon/att/tmobile/ and use it as prepaid. But it can be more expensive.
Oh and look at the best answer on this question it might help as well.