I might not be the best person to answer this as I haven't lived in Denver very long, but I'll give it a shot with what I know.
When I visited here I got a great deal on a hotel through Priceline. I got the Hyatt on Welton for less that half price - I paid like $90/night, but different year, different season. Anything downtown will suit your needs. I can't think of any hotels that are right next to Coors Field anyway, and within a few blocks in the wrong direction it gets pretty sketchy so you're better off looking at downtown - 16th street & Welton has a few 3 & 4 star hotels. make sure to check with the hotel to see what the parking charges might be - I doubt it's free. You won't need a car anyway if you're downtown.
From there you can take the free bus up and down 16th street all day long - that's what the tourists do as far as I can tell. At the bottom of 16th, it's a short few blocks to the stadium, with plenty of bars along the way to keep you busy. Don't bother with driving or parking if you already have a place downtown.
For other activities, there is a great art museum (never been there but they tell me it's nice), 16th street mall has tons of stuff to do, Red Rocks... I dunno. Mostly people here just drink so there's lots of that.
