Need room on rent.

Living in Bukit Bintang is best option. Cost of room will be rm1-1.5k per month

Mont kiara has no train and bad transport connections.

Check on www.ibilik.my for other ideas

How much time does it take from Bukit Bintang by lrt or mrt?

Inside your travel time limit as 5 stations. But not sure how easy to reach office block from MRT station

Bangsar Shopping Area has some room rentals nearby and T850 bus direct to building area. It goes from LRT Bangsar which has Gaya Condo right on the doorstep and sometimes unit sharing available there. But generally speaking Bangsar is overpriced for everything.

Brickfields also possible but not sure how long the walk would be to the MRT line station (it's a new line since July 2017).  Brickfields is of course "Little India". Room rentals will be a little cheaper but in oldish buildings.

From Brickfields to nearest MRT is Muzium Negara MRT Station, however to reach there you ,need to walk till KL sentral and inside Kl sentral there is way which goes to MRT station and from there 5 to 7 mins walks follow sign for MRT you will reach MRT station.

Or if you don't want to walk then from Kl sentral stesen opp hilton hotel there is bus stop from there you can take free Go KL red line bus from kl sentral stesen the next plaza sentral 1 then Muzium Negara next to it is MRT it will take max 4 mins  or less.

just shared what i was aware of best of luck.

You can also create account on http://www.ibilik.my/  in search type select  the place which you intend to stay it will be all list properties for rental.

Also you can search in www.mudah.my for rental .