Agreed those screw-driver adjust trimpots would work in this case. It's just that USPS First-Class shipping from DigiKey starts at about $5. So if that's all you're buying from DigiKey, a couple 78 cent trimpots balloons to $3 a piece! On eBay you can do a bit better but the underlying problem is you are forced into USPS First Class package rates since the trimpot size means a package >1/4" thick. OTOH you can mail 1/2W fixed resistors using regular USPS envelope rates since they are thinner than 1/4". Probably too much information but I really don't feel comfortable spending other-people's-money! 
