DWM excepts only cash but his prices are the cheapest I've found on the island, my wife and I dove for 6 days, 2 tank dives each day and with a 10% discount I think our bill was around $475! plus we got a free night dive and a free video out of it.
Good DM'S, good prices, 8 or less to a boat, they have nitrox and magnum tanks I do believe. visit his website
www.divewithmartin.com for more info, if you e-mail him he'll get right back to you.
I looked at his website and it says that 5 days of 2 tank dives is $250 (and that includes the cash discount). When were you there, and do you need to ask for more off? I would like to dive for 6 days as well. Thanks.