Plain old Hydrogen isn't terribly good for fusion reactors. Not enough neutrons in it.
You need to pull the minute amounts of Deuterium and Tritium from your collected gas, and that is where the big costs would come in.
http://www.webelements.com/webelemen...xt/H/isot.html
(Tritium has a half-life of only 12 years, and thus isn't in the chart). Neutron bombardment will make you some.