(reply to OP)

Money pit -

Not really. Right now, you have to decide if you will spend money on labor or tools. Ultra cheap is single speed it by losing all derailers, and picking the front / back sprocket combo that suits you, and string the chain to keep it as straight as possible. On a double, that's usually the inside front (42) and the third rear sprocket (16 or 18).

Tools needed - Chain breaker, $10
Options - new chain, BMX freewheel, $30 combined

I don't know how the chainline would look if you removed the old freewheel and added a new BMX fw. I think the hub is English thread, but not sure on that.