A cheap way to finish wide boards / table slabs etc is to use a router bridge.
Basically you have rails on each side of the board, and some sort of bridge between them. The router gets run from side to side and moved down the board and everything above the heigth of the bit is shaved off. A large bowl cutting blank seems to work best.
The finish wont be perfect, but it will be totally flat which is the hard part. Then you can just break out a hand sander and finish it off.
For boards under 12" a portable planer is a better option. I have a DeWalt 733 unit that has served me well. There are cheaper options out there that work fine as well.
A jointer is usefull if you are trying to do any precision woodworking as they let you put a perfectly straight and 90 deg edge on your board before you start planing it. But a jointer by itself is pretty useless as it has no way of getting the opposite faces parrallel. You can joint a board by other methods if you need to, hand plane, router / straight ege / bridge or buy building a sled for your planer.
Here is some pics of my router setup - I have cheated and just mounted the router on my sawmill, but you can make a simple version in shed
This is a fish tank stand with a 24" wide top finished with the router setup above.
Cheers
Ian