So my wife and I did our first organized ride in the rain this weekend in San Diego and the wet weather really wore down the pads on the caliper brakes(whatever comes on the non disc brake cannondales). The brakes ended up failing to the point where we weren't slowing down and after unintentionally running a red light I had to unclip and dragged my foot to stop. After waiting an hour and a half at an REI we bought some new brakes but they also wore down quite a bit and were squealing an obnoxious amount (wife was very embarrassed). We plan to start doing some multi day touring (Glacier Park this summer) and want to upgrade the brakes. I really don't know anything about bikes so trying to find the most cost effective way of upgrading the brakes. Also our brakes are currently setup so they are both applied with the pull of just the left lever (there is no right brake lever on the bike and I've read that might make a drum brake a good option).
I really just want something that can be quickly added at a fairly reasonable cost (would like less than $300 as that would be a third of what we spent on the bike). I went to a local bike shop and asked about disc brakes and they told me I would need new wheels and was looking at well over my desired price. I've looked on precision tandems website based on some other posts and was wondering if the disc kits would work (not sure about the threaded hub bit).
If someone could give me some advice (if it is possible at the desired price) and a website with instructions and where and what parts to purchase it would be greatly appreciated.