It really just depends on what you're looking to do. Vail is a HUGE ski town this time of year, so while it's got plenty for people to keep busy who aren't skiing, you're going to be competing with the ski crowds for hotel rooms, restaurants, etc. That's why your prices are going to be sky high.
Estes Park, on the other hand, isn't going to have all of the high-end shops and such that you might find in Vail, but Estes is actually fairly quiet this time of year. You can probably find some really good deals on lodging, and most of the shops downtown are open as usual.
So, between those two, if you're looking for a quiet getaway, Estes Park is going to be your winner. If you're looking for an active mountain experience that will have tons of stuff for you to see and do, Vail is going to be more your style.
If you're looking for something kind of in between, Breckenridge is another option you might look into. It's a ski town, but smaller than Vail and (in my opinion) more quaint.