My parents want to stay a 6 months a year in thailand, I living also in thailand, and use bkk as there base for their travels around thailand/asia.

They like the kao san road area so they are looking for a appartment or hotel where they have okay monthly rates, arond 40000 a mnth

there isn't much in the way of decent apartments around khao san road- the best one I found was Juldis River Mansion- take Samsen Soi 3 all the way back to the river (near the Phra Sumen park) to find it.

Here is a list of others in that area...

Not actually at Koh San, but across the bridge is Rattana Kohsin.  The beautiful pool there is in some sort of problem situation, but there are some nice apartments for rent there, and the views of some of them are fantastic.  Rattana Kohsin is right across from the Kata Department Store, so it is fairly convenient.  Koh San is a two minute taxi ride or a 15 minute walk away.

Not actually at Koh San, but across the bridge is Rattana Kohsin. The beautiful pool there is in some sort of problem situation, but there are some nice apartments for rent there, and the views of some of them are fantastic. Rattana Kohsin is right across from the Kata Department Store, so it is fairly convenient. Koh San is a two minute taxi ride or a 15 minute walk away.

That place was great. Pitty the people who ran the fitness club didnt pay their bills and just left. What was once a great pool, is now a mosquito breeding ground.