There have been a few threads on this if you search, but I could never find a place downtown to park that was not the standard car rates; which were too high for me even for a car. Ended up parking at the light rail station at I25 and Broadway where they have free motorcycle parking, then rode the light rail down.

Also tried the "well if I have to pay for a car space can I get at least one other (maybe even three) motorcycles to split the cost and space with and we will share the spot....all told me no and one space one bike.