Decade variable resistor 0 - 10Mohm* in increments of 1ohm with a laser cut enclosure using moderately cheap and easily sourceable components.

Total cost for the parts orders looks to be just under $40 plus acrylic ($10 for a 24"x18" at Lowe's), but this doesn't take into account the fact that, e.g, while you are ordering 100 bolts, you are only using 12. Real cost is probably closer to $15. The soldering is rather tightly packed, so proceed at your own risk.

A word of warning: I designed this mostly for myself, so don't assume that everything will be perfect. I may also refine a couple things in the coming weeks.

A note about resistor tolerances: I'm using 1% resistors. I wanted something better than the really cheap and common 5% resistors, but much better than 1% costs too much. Also, the switches themselves add resistance and some variance. The tolerances don't add like some people worry for setups like this - any resistance I can dial in will be within 1% of the number on the switches - in theory. The switches add a couple ohms (1.5ish) to the box overall, so the low values will be more imperfect than the high values. Also, it's best practice that once you tune a circuit with a box like this, you remove the box then measure the resistance instead of relying on the readout.

If you just want a decade resistor instead of taking the time to do it this way, Sparkfun has a kit for $30 that'll go from 0-1M with 10ohm increments. I like mine better.

*Yes, I'm lying to you. It actually only goes up to 9,999,999 ohms.