How much would a 3 month backpacking trip through Thailand cost?

You may get a ton of answers but please give us some answers as to your desires and budget level. If you want to go minimum without cock roaches you are talkin a room at about 600 - 800
Thai baht in Bangkok and knock of 100-200 out of town. You can split this with a friend so that it is even cheaper. $1 US is about 31-thai but give or take. (Don't know your currency) Splitting a room is $10-15 each. Yes you can go cheaper by $5 but you get what you pay for. People will try to brag how low they went but some places are dirty and disgusting. Food can be cheap if you eat Thai. You can get Phad Thai on the street for 20-30 baht or 100-200 baht meals. Noodles can be 20-30 or up to 80 at a nicer place. 20for a can of coke or so.
Realistically you will want to travel. I say for a month with a pal
$400 US for room $300 for food. $100 other. That is $800. You can really go low with $500 but you won't have any wiggle room. I would take $1000 for a month and relax more but do your own thing. Lonely Planet's website forum has tons of threads on this.

i did it for 2 months 3 years ago & on average i spent around usd980 per month and i travelled extensively and did many things. so now,on the safe side, usd1200 per month.

i agree totally depends on your standard level, i travelled around fine for around 拢15 a day inc accomodation but then i didnt drink lots and didnt mind if i had fan instead of air con and the odd bug friend for company! my rule of thumb was if it had a hammock it was ok!! but 拢10-15 plus beer money! but for that expect to be taking coaches not little internal flights everywhere, there really cheap, you norm get lunch thrown in and can be very funny! enjoy x

Hi I am heading back to Thailand again in March for a three weeks traveling on a budget as always.

Here is my daily budget:-

Accommodation...... $12 aud
B/fast and dinner..... $5
Moped 125 yam...... $6
Couple beers........... $2

That amounts to $25 a day.

I will allow about $200 for train fares which will take me north south east and west.
And $100 for buses that will get me where the train wont.
Add another $50 for taxis and tuk tuks that I rarely use.

Thats around $850 for three weeks.

I will take an extra $650 for "extras" that may take my fancy,
and will be sure to still have around $500 on my last day.

I always take my plastic for 'You never knows"

I know your going for three months (lucky you) so you will just have to do some sums.

Have a great trip. I know I will.

You can stay in some pretty cheap places in Thailand.

I allow about $30 a day - staying in places for a few days at a time.

Vegetable stir fries with rice are your cheapest meals!