I looked around online and here is what I found:
- There is a "complete system" that sells for over $700 (list price of $900) like this one here: Portable Tank Cleaning Kit
Now, just to be sure I searched around a bit. It appears that all the parts for this system are available retail:
Pump - 12V DC Gear Pump
Filter - Clear Bowl Filter Kit
Strainer appears to be garden variety, probably $15 or so at any store.
I am of opinion that those Algae-X devices are gimmicks and don't do anything, so no cost on that.
Total in parts - $200 or so, plus a few hoses and fittings (and some sort of a board to set it all up on).