Airport code is STV.

Then get out KVS/Sabre.

There used to be flights by most carriers from BOM, but nowadays doesn't show any flights! (Jet/IT/Indigo were all once flying there, as I recall)

However, now your options are either by train, bus or car.

I would recommend doing the safest option, by train.

Indian railways website is here (www.irctc.co.in), which is the cheapest option, or you can use Cleartrip, which is much easier to use and shows you most of the trains plying to STV (From BOM (or BCT, the railways code for Mumbai - or Mumbai Central Station).

Cleartrip: http://www.cleartrip.com/trains/search