Hi Melissa,
I have been to Thailand twice for FFS and SRS.
I have spent very little money both times outside of the surgery costs.
Accomodation is relatively chesp, My Hotel in October was $25 per night (and if you check out for the 4-5 days when in hospital) can be even cheaper. Food is very cheap, I spent < $10 per day and if you have a hotel with a buffet breakfast, stock up for lunch. Sharing a room can reduce the cost.
Other expenses are very cheap, I got my washing / ironng done every 3 days or so for about $1, which included hangers andwrapping in plastic cover!
Phone cards are cheap, about 400 Baht upwards and this is a better option than people calling you as you will be charged for the mobile call while overseas for using Thai Telecom services.
Internet acces is fairly cheap, I used an internet cafe, cost was about $3 per hour. I also used my lap top with Dial up access or wireless access where I could. If you have access to Skype, phone calls are cheap as well.
Taxi's - use the local taxis and you can agree the price, when you get in the taxi.
Excursions - You can get very cheap days out, lots of people know people who will take you (for a small fee) to various tourist attractions. I went to Tiger Sancturys, Nature reserves, palaces, River cruises and floating markets... all great attractions.
On my last visit which was for 16 days I spent < $1000, which included presents and momentoes.
REMEMBER .... to keep 500 baht in cash as this is the Passenger Airport Tax, required to leave the Country. I have heard it may be 700 Baht next year.
Buffy