Fair trap costs

[Jeff the Green]

I've been working on revamping my Inspired Inventor (http://www.giantitp.com/forums/showthread.php?t=273831) homebrew PrC, which has the ability to create a gadget that fires off mechanical traps (that never reset). Originally I'd thought of pricing it based off of the trap's normal price, but then I looked them up and realized that they're really freaking expensive. Is there a better way to price them?

[Spore]

Here's how PF handled it (http://paizo.com/pathfinderRPG/prd/ultimateMagic/spellcastingClassOptions/ranger.html). Keep in mind that they traded in spellcasting for this.

[Jeff the Green]

That's very similar to the combat trapsmith's booby traps, and not what I'm looking for. I'd really like it to be able to create arrow traps, etc. I just can't figure out a good way to price it.