Rubberduck,
There are a couple fields near Sioux Falls, and I encountered friendly folks at both. I think if I'd had a plane with me, they might have let me fly. Why don't you try going & asking?
The guys who fly older style planes are very nice, and would probably help you. They belong to some organization that goes by initials that are something like "SAM", for Society of Antique Modelers.
The other field only had one flier present, at the time, and he was friendly too.
My point here is, club people all went through what you're going through, and understand. They also have experience, and can help you preserve your investment. Having visited Sioux Falls and met some of the people, I'm inclined to advise you to contact them first, before you try to fly alone. I guarantee the experience will be helpful.
Good luck,
Dave Olson
ORIGINAL: Rubberduck
I realize that the best place to fly is at a RC "airport", but all of the fields around here belong to clubs that require a yearly membership to join. Being that it is near the end of the season, I really don't want to pony up the ~ $100 (AMA membership, club dues, field rental, etc) that it would cost to fly on the final few days of the season.
So, what would be good alternative places to fly? There are a couple of big city parks around town where they play soccer, etc (i.e. no trees) that I could use, but I'm looking for some other alternatives.