bangkok hospital and places to stay

I need to come to Bangkok to see a doctor who works at the Bangkok Hospital, apparently also known as "Bangkok Heart Hospital," on Petchaburi 47.

I have spent more time in Northern Thailand and do not know Bangkok well but my understanding is this hospital is somewhat removed from the main city and that accommodation available nearby is quite pricey by Thai standards. Since I imagine most people staying in that area are foreigners visiting Thailand specifically to go to Bangkok Hospital, this doesn't surprise me. But if anyone knows of a place there that is cheap and decent, I'd be glad to hear about it.

Since I will be in the city more than a week, I would like to find a relatively inexpensive guest house (500 baht or less). It doesn't need to be in the same area as the hospital, but I'd like to be somewhere with convenient transportation to the hospital, because I anticipate I may need to make 2 or 3 trips there.

Anyone have any suggestions on the best option for my situation?

Thanks for your help.