There is also Denver Meadows RV Park off I-225 between I-70 and US-40. They don't have a limitation on how long you can stay, but it may be more than you want to spend. Last year's daily rate was $33.
If you are planning to spend 2-4 months, ask for the monthly rate. It is usually less per-day than the daily rate. Most campground managers prefer to have the steady income and will offer a discount.
info@denvermeadows.com, (303) 364-9483.