Question: How much does a jointer cost?
Answer: Nothing, when you make it out of scrap.
Seriously, jointers can run some cash. I saw a reconditioned one awhile back for around $250. It had a 6 inch capacity and was a bench top model. The bench top part of it means it saves on some space, but the 6 inch capacity is a little deflating.
Plus a jointer only has one purpose in life. Joint. In a small shop you need your tools to pull their weight and perform multiple functions if need be. I have issues with large bulky machines that only perform one task. My psychiatrist tells me so.
3/4" MDF for the base
5' or 6' of 3/4" thick furring strips for the hold downs and miter slot runner
3 wing nuts
My suggestion is to find whatever you have in your shop that will work. The MDF was left over from a 4x8 sheet I have had sitting around for years. Anything stable and resistant to warping would work. The furring strips were cut down from 2x4's that have been left over from previous projects. I have gotten so much mileage out of these furring strips that I now grab every stray piece of 2x4 I happen to see around town.
The bolts, washers and wing nuts all came out of my Miscellaneous bin. You know those items you buy and they come with their own mounting hardware. Often times manufacturers will give you several options for mounting. So you end up with left over hardware. That is were these came from. I wouldn't even be able to tell you when or from what these came into my possession.
The bolts had a very wide head to them eliminating the need for a washer on that end. Bolts that do not have a wide head should have a washer used with them to help distribute the pressure exerted from the tightening process. This is separate from the washers used on the wing nut side.
Hold down arms
A few notes:
The holes that are drilled through the base should be somewhat oversized for the body of the bolts used. This gives the bolt some wiggle room so you can get thicker stock under the hold downs. You could also elongate the holes in the arms to achieve the same effect.
I have an 8" capacity on this set up with these measurements. A wider jointing capacity could be achieved by widening the base. Also, the length of the base was arbitrary. It could be made however long or short you needed for your needs.
Happy DIY'ing and stay safe.