UDC is a very good shop, but mainly tuned into the dive school thing. I have not been to Deep Blue's resort, but it appears to be the typical all inclusive Dive Lodge, similar to Laguna Beach, where I have been on two trips. Deep Blue gets a lot of positive comments around here.
Doing UDC with Mango puts you somewhere price-wise between staying in a backpacker place and using one of the in town shops like UDC, and staying at Laguna or Deep Blue. That said, Mango has nice landscaping, good food, A/C, and a nice pool, even if it is back from the water.
I enjoyed doing the backpacker thing with UDC last time, but would almost certainly go to one of the resorts if traveling with The Mermaid, but that reflects both her tastes and a woman's ability to get her way. Most of the other customers on the boat with me were staying at Mango, and I did not hear any complaints. The resorts are fairly dead by 9 pm, and not the best place to stay if you like to go out drinking or generally raising hell in the evening. Dives at the resorts will be slightly longer, but not way longer as the kitchen staff does not like to wait around forever.
$500 each, that depends on how dear cash is to you, or how deep in hock you are willing to get to take a vacation.