I haven't seen a usable recipe for home made fountain pen ink. The better ones are for iron gall ink, which when home made, is too corrosive for fountain pens.
If you really want to write cheaply, then get some dip pens and ink powder, such as in
this auction. The ink powder will make a quart of ink with each packet. The nibs aren't that hot, so you may want to look around for other, better vintage nibs.
The ink is too thin to work in fountain pens, or with modern dip nibs, such as those by Hunt or Nikko.
Alternatively, the eBay store
ink4pens sells inexpensive cartridges. If you need a matching pen, she sells those, too. I haven't tried them, so I can't comment.
Another alternative is to look around for bottles of ink on eBay, such as
this one. A dozen bottles (even at about 1 oz each) should keep you writing for quite some time...
I haven't tried the vintage Sanfords Penit ink, so I can't comment on it for quality.