I'm thinking of using some of thegadgets from spycraft in my d20 mod game. i was thinking that it would be as easy as just assinging a dc check for price but wanted some advice in case i'm stepping into a big mess.
Check out this thread. I've converted several gadgets and vehicle modifications from Spycraft to D20 Modern, but that thread has at least one vehicle modification that I brought over from Spycraft (though I also changed it up a bit). It's not hard. Basically, you just need to come up with a dollar value and slap it on.
For example, in the case of the Purchase DCs for my vehicle modifications, the DC takes into account labor costs, parts, expert craftsmanship (not to be mistaken for mastercraft), and the guarantee that it will work reliably (unless specifically stated otherwise in the description of the modification).
However, these DCs also reflect the cost of having someone else do the work. If you're doing it yourself, you basically only need to pay for the parts, and tools (if applicable). You don't pay for your own time and labor, as that is already factored into the skill check. Also, if you're not making any of the parts from scratch, i.e. if you're just putting it together, you use the Repair skill and not the Craft skill. The Craft skill is used when you're building something from nothing. For example, building a computer from complete scratch is expensive, as you're actually building each component yourself. When you order all the parts from somewhere else, such as the case, MB, HD, GC, etc, you're now just putting them all together.
Essentially, if a character is doing the work (i.e. just ordering the parts and assembling it), then you, the GM, might decide that the Purchase DC is lower.
For items such as that, you'll pretty much have to guesstimate their value. Remember to price a gadget based on its usefulness, but more importantly, remember not to give something an unjustifiably high price. If you can't logically explain why a gadget (which is not a collector's item in the traditional sense) should have such a high price, but you truly feel that the item must have such a high price because then everyone would want it, then there is a fair chance that the item probably is just too good. Also, it never hurts to seek advice here.