I'm putting together my first firing panel and need a little help in picking the right size wire for the slat cables.

The setup as I envision it right now is as follows :

24 volt supply (maybe 48 if that will help keep the wire size managable)
Firing home-made chip style ignitors (as described by Skylighter and FireFox)
Max length between panel and furthest slat would be 200-250 feet
Leaning towards db type connectors (25s most likely)

I'm wondering what the best - and most economical - choice for wire would be. Reading through the old threads gives me the impression that 20-18 gauge would be best. Is this correct?