Mile high Music Festival, Denver

[Don]

Josh and I just decided to road trip out to Denver tomorrow after work in order to see the Mile High Music Fest (http://milehighmusicfestival.com/). (and maybe one of my army buddies if he can convince his wife to let him go).
The concert is in Commerce City (Denver suburbs?) Saturday and Sunday (19-20 July).
We haven't planned this out real well but plan to stick to a budget.
Anyone recommend a nearby campsite (legal or otherwise), maybe a dark city park or something?
Or is anyone in the area willing to let a couple of respectfull, quiet, non-felons crash in their backyard or horse pasture Saturday and Sunday nights?