I think the market is going for RM4-6 psf.... some crazy designer who aren't even reputable asking for RM10-15 psf...
Honestly don't bother with interior designers.... they are a waste of your time...
if you want to design a 1,000sqf apartment... the design fee alone costs at least RM4k which is beyond silly.....
The main reason I said that is because even though you are designing for a 1k sqf apartment... it mostly leaves out foyer/yard/toilet and even general spaces.... you most likely end up with a 600sqf of actual artist impression...
they end up just "decorating" your house rather than actually designing it....
and you know the silliest part about all these??? They got the audacity to argue about the cost for studying interior designing at university.... saw 1 idiot on this forum back in 2012 says it costs RM400k to study his degree but the dumbest part is he includes all his cost of living in the UK..   

a typical ID degree is no different from any other 3 years degree (excluding medical studies)....  you don't see them graduates going around asking RM4k for 1 day worth of work don't you...
They are literally charging like developed country rates but does not have that developed country ID's creativity...
In conclusion... unless they are just charging you a flat rate of RM2k for a typical 1k sqf apartment... just skip ID all together unless you are filthy rich and money is not an issue...