Replacing cables and housings is actually really easy once you get some exposure to it. Once you understand how the derailleurs shift and how the shifters make that happen (cable tension), adjusting them becomes extremely easy. You could check to see if your LBS has a maintenance clinic (my lbs has a clinic every wednesday night), and if not, a great guide is Zinn's Art of Mountain Bike Maintenance. You should be able to find it at a Borders or Barnes and Noble. I bought it last week and have been reading through it as I have time - it's very informative and really breaks things down.
are your cables fully housed or only partially? if they are not fully housed i bet you just need to clean em off/ dry em off. if this is the case i would reccomend going to LBS and getting some housing to cover them completely and zip tying them to your frame. if you have a LBS do it then it should be pretty cheap 25$ 35$.... or do it yourself and learn somthing knew. you can always take it to the LBS later.
If you know how to adjust your derailler(If you don't, it's not hard, read the manual and be patient), changing cables is easy, just match your current housing lenghts and thread them in (make sure the lining of the housing is opened up, an awl works for this). I highly doubt the cable would cost more than $20 at your lbs. When my x-9 was jumping around on me I found that the wire lining of the housing was coming apart and dragging on the cable, new ones fixed it. Look for a plug on you shifter that allows you to pull the cable out the back (sram anyway).
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