Rust bluing (slow or hot water) can be accomplished with minimal materials and aluminum oxide paper for polishing. You don't use finer than 400 grit because the bluing process involves constant repolishing with steel wool.
The resulting blue is harder than salt blues and just as lusterous, but requires more effort. Total cost of hot water bluing is about $60, since all you need is the oxide paper, the chemical, a pot big enough for the piece(s), steel wool, a stainless steel brush, gloves and degreaser.
The slow process requires a little less elbow grease, but more time (a week or more) and a humidity cabinet. The hot water process takes few hours.
This is how bluing was first done. Salt bluing is a much more recent process that isn't as durable but less labor intensive. Brownells can set you up with what you need in two different formulas. I'm very pleased with my results.