Byuing that kind of size land near the city will cost you a lot. If you are ok about driving for 10 mins to go to Big C then you might get ok land for about 300K Baht per Rai (which is 40x40 metres).
I am looking into buying land to build a house myself and there are some things you should be aware of:
- Rice field land is very cheap but need a lot of sand filling which you have to do before the rain season for it to settle. Also you have to think about the availability of el.power and water which will cost you if it's not already there.
- Possibility of telephone and internet (it's not common here quite yet)
- To make a road connection to your house will cost you A LOT also if you don't make the deal BEFORE you buy the land (you'll have to buy land for the road, and if they know you need it, you'll bleed)
- Location is relatively extremely expensive in Thailand, so if you can stay a little bit outside the city you will save money, just make sure it's an area where there are telephone lines already(a friend bought cheap land a little bit outside and they're talking about 140K just to make a phone line and internet)
-Typically, good land with access to road/electricity/water/phone just a little outside should cost not more than 300K for 1 Rai (with a good view

)
- The price of the house will depend on the standard you want offcourse, a one-floor thai-standard house with three bedrooms costs about 500K Baht to put up. Then you have concrete and tiles, no kitchen (backside thai style), also simple bathrooms, and an el.system that needs modyfying for farang style living. It all depends on the quality you want but in my opinion a good house with 3-4 bedrooms will cost between 1 and 1,5 million Baht.