Firstly; expect everywhere that isn't a complete dive (and some places that are) in Mumbai to be very expensive. Once you've accepted that, you'll find that the ISKCON centre, whilst definitely being pricier than what you'll expect to pay for similar quality in most other Indian cities, is actually something of a bargain in Mumbai!
For a start, the rooms are HUGE. We stayed in the newer wing of the guest house (recommended!) and our room was pretty cavernous... the biggest we saw in all of India! And it was completely spotless, as was our nice (and also very big) ensuite bathroom. The room was also filled with pretty painted furniture, the beds were comfortable and new, and there were lovely big windows to let the light in.
the guesthouse itself feels more like a hotel than any kind of hostel, from the classy check-in area to the 'guards' (who are incredibly friendly and double up as general customer service assistants) posted on each floor. the massive staff presence around the ISKCON centre, as well as the high compound security at the entrances/exits to this very well guarded complex really make you feel safe - just what you need if, like us, you have just arrived into the jetlag and culture shock of India.
there's also lots going on around you in ISKCON - it wasn't uncommon for us to walk out of our bedroom door and into a procession of beautifully dressed, jewel-covered girls tinkling down the hall towards one of the prayer rooms, or to hear singing and chanting through the windows from elsewhere in the centre.
i think the location of the guesthouse (i.e. out in the Juhu suburb rather than in the city centre) probably puts a lot of potential guests off, but i would say that this is actually a strength for ISKCON rather than a weakness - the suburban location means you get more room (and better quality accommodation) for your money, and it's also a quiet and non-touristy area to stay in, away from the chaos and commerce of central mumbai. Also, it's really not that difficult to get into town... you take an autorickshaw to Vile Parle (the nearest metro station) for about 20R (it's a 5 or 10 minute ride - if you've got time on your hands it's even possible to walk it) and then it's a quick, cheap and interesting suburban train journey into the town centre Churchgate station. coming back at night is no problem either - the trains run til after midnight, and there are always rickshaws waiting at Vile Parle (just watch out for the immortal "100 rupees" foreigner trap amongst the rickshaws... it's definitely not more than a 25 rupee journey).
There's also a really fab (slightly pricey, but completely worth it) restaurant downstairs in the ISKCON centre...i think it's called 'Govindas'. you pay a fixed price, then start with a kind of all-you-
can-eat buffet, and then the waiters literally heap all manner of drinks (non-alcoholic of course) and desserts onto you for the rest of the night. the gulab jamun are particularly good...you won't be able to move once you've finished with that feast.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.