Jared,
Check out the long list of custom Gun Builders I just put up on a website I did. Several of them sell their trigger sets but I doubt they are any cheaper than Riffe's - probably more$. Browsing all of these custom sites will give you serious gun envy but will also inspire you and provide resources for other small parts you might want. A Few of these guys sell do it your self gun kits but it sounds like you already have a good start. The website is
www.SpearTrips.com then go to "Misc Info" and then to "Speargun Links". Don't skip Internet Custom Spearguns for parts. Actually I wouldn't skip any of the U.S. sites.
Good luck and have fun!
Robbert
Robbert@SpeaTrips.com