You have to compare expenses with income. $100 a week does not mean anything. A lot of people here have contributed $100 a week to church groups that have not survived here.
Why are they renting the parking lot if they don't need the money?
It is important to understand the reasons why they are doing something and offer solutions. If reasonable solutions are not at least entertained, or people do not comprehend what they are actually doing in the first place, then I think a protest is appropriate.
I do think it sucks not to be able to part at your own church though. Does evidence suggest they are simply greedy? Are they being good neighbors? Do they realize people cannot park at their own church?