How to determine whether EC is fairly priced.
1) Looked at the psf of the EC versus the surrounding new private developments as well as old developments. Make sure the EC size you are buying has a discount of at least 15% from the private development size(equivalent or thereabout). You can factor in the grant to make the calculation.
2) Looked at the rental amount(dont look at psf) of the equivalent unit (3bdrm vs 3bdrm) in surrounding private developments again. Then use your intended EC purchase price divided by the rental*12. You get the gross rental yield. Determine whether the rental yield is above or in line with the existing developments.
If both these conditions fulfilled.. it is fairly priced . then it's up to you to decide on the qualitative factors like near school.. nice environment, good transport etc. whether the place is what you like.
as for affordability, you just apply the TDSR and MSR and whatever MAS imposed . MAS has already done the homework for you to make sure prudent leverage is used. You follow. If you are stretching it with their TDSR,MSR .. then that unit might not be affordable to you.