I was in the same position, thinking of the cheapest for a scanner.
Thing is, they aren't cheap at all. Just a good DAC will set you back $300 USD. And a basic ILDA scanner will cost $300 USD too.
In the end, I've settled on a great 130mW 10kpps RGY scanner for $350 shipped, and a good quality DAC for $360 USD. (Oh yeah, the DAC was more expensive than the scanner!). $710 USD all up.
You could probably do the same thing for $500 USD.
-Galvos:150, l
-lasers:150 (you already got lasers, but you had to pay for them some time!),
-sound card dac:100,
-optics + case + wiring + misc:100.
But you'd have to be pretty competent at electronics and building, plus the free software would never be as good as bought software.
With low end, entry level scanners it might be easier to just to buy them I've found. Where it comes cost effective for DIY is when you're making some serious scanners, like a 1 Watt full analogue RGB or something. Buying that new would cost heaps, but DIY would be much cheaper (that's what I'm doing
).