We've used www.pvrpv.com in the past and were very happy. We especially liked the fact that they took credit cards, and met us at the condo on arrival. We loved the place that we stayed - Selva Romantica - but I'm not sure it will meet your budget. I don't think that you'd have trouble finding something for $100/night in April.

I have a friend who seems to spend most of his free time researching (and booking) condos in PVR. PM me if you would like more info.