Prices for "reasonable" quality and "reasonable" location in Bangkok is 70.000 - 90,000 baht/sqm (semi-furnished). Examples of projects are Noble Solo, LH Room, and Sansiri Cell. But if you want what upper middle class Thais buy, you have to cough up 10-20% more. The major developers in Thailand normally offers/markets projects in 2-3 different price / quality segments.
Here's some perspectives on the market:
http://www.thailawforum.com/condo-and-real-estate-in-thailand.html
Below are links to projects in the
Amanta Lumpini ... problem with that location is that a few years down the road the Central Group will have erected a new shopping mall where the Lumpini night bazar was.
Chamchuri is located near Chulalongkorn University and Siam Square. They have some units at 69.000 baht/sqm (unfurnished)
Belle looks good, but is located in an area with terrible traffic jams. Prices are therefore a bit lower - starting at 59,000 baht/sqm while two years ago, the prices were 50,000 baht/sqm. The pros and cons are discussed here
http://www.prakard.com/default.aspx?g=posts&t=72588