really, you need at least three finish tools, wood, mag and steel.
1.- wood (doesn't have to be a nice storebought one, it can be pretty much anything.) to get your rough shape. i know some dudes who are all about making custom fiberglass floats for specific stuff, too.
2.- a magnesium float to help compress the aggregate, and bring up the cream. this is crucial.
3.- a steel trowel (not the shitty square one, but a rounded pool trowel. they cost more, but it's worth it to not have the corners of your trowel fucking you up while you're trying to finish.) to "burn" the concrete.
but if you're super broke, and can only afford one trowel, i'd say get a mag. at least then you'll be bringing up some cream.