WalMart TLE says I need to service my transfer case.  Googled and learned that means replacing the fluid around some gears in a box somewhere.  How much should this cost and how often should it be done?  Dealer webpage I found said every 30k.
Thanks!
J

Year make and model + mileage would be helpful here, but I'll take a stab at it.  Most manufacturers recommend servicing all driveline (differentials, transfer case, transmission) AT LEAST  every 30 months/30,000 miles.  I do mine more often that that.  
Making the assumption you are driving a 4WD with auto trans, Ford/GM/Dodge, and have about 30,000 miles:  Service (fluid exchange) front and rear differentials, transfer case, and flsuh the transmission and replace the filter. At 45K, flush the transmission and service the rear diff again.  So every 15K interval the trans gets either filter or fluid exchange and the rear diff gets new fluid.  Coolant, again depending on manufacturer, is good for varying periods.  Don't buy into the 100,000 miles and no service hype.  Monitor and replace ALL FLUIDS as needed, including power steering and brake fluids.  
FWIW: I am a service writer for a Toyota dealer, have been writing for almost 20 years for a variety of imports and domestic brands, and ran two trans shops for four years.... my recommendations are in excess of the manufacturer's based on personal and professional observations.  
If you want to get more specific, email or IM me so as not to clutter up the board too bad.

1911fan

Is there a special hell for people who don't service their cars nearly enough?
'02 S10 4WD ~62k miles
I had the transmission and coolant serviced earlier this year (first time, figured it was a good idea).
All righty then, I guess I'll set up an appointment to get this done.

Quoted: Is there a special hell for people who don't service their cars nearly enough? '02 S10 4WD ~62k miles I had the transmission and coolant serviced earlier this year (first time, figured it was a good idea). All righty then, I guess I'll set up an appointment to get this done.

Or make a trip to AZ and DIY.    This is basically an oil change, nothing more.  

Quoted: Is there a special hell for people who don't service their cars nearly enough?

Yeah, and it's called service writer heaven.... of course it broke, you didn't maintain it, and here's what it takes to fix it.  KA-CHING!!!
I'll give you the same advice I gave my sister, who lives a long way off and was having constant truck problems for years.  Find the nearest convenient dealer and go there for everything.  Most dealers have a quicklube setup too.  Always deal with the same service writer.  Take a box of doughnuts in every third or fourth trip and leave them on teh seat wth a note that says, "For technicians only!" and request the same tech every time.
If you don't like that dealer, go to the next nearest one.  Yes, it costs more.  No, it's not as convenient.  Your truck will last longer though- what's that worth?
Oh, and read the owner's manual.  A lot of the preventive maintenance info is in it, and it sounds like you are a bit behind.  It's catch-up time.  KA-CHING!!!

1911fan

Quoted: WalMart TLE says I need to service my transfer case.  Googled and learned that means replacing the fluid around some gears in a box somewhere.  How much should this cost and how often should it be done?  Dealer webpage I found said every 30k. Thanks! J

First do not take your truck to one of these fast food auto shops. (wal mart, jiffylube, whatever) I made the mistake of accepting a job as a manager at a wal mart tle. Those idiots tried weekly to give me an anyeurism. Get yourself a real mechanic, use the same one regularly or learn how to do it yourself. Go to your local parts store and buy the correct "haynes" manual for your truck. Changing your transfer case lube is one of the easiest jobs on a truck. Do it yourself, save some bucks and learn.

T case is easy to swap fluid. Also consoder front and rear diff fluids too(axles) . You are far more likely to have diff fluid issues than t ccase unless you have water in the t case.

If you take your truck swimming as often as I do my Jeep then plan on changing those out a lot sooner.