Bicycle Mechanics - maintenance or replacement

I brought my CAAD9 to my local shop.
They will tune up, clean and replace some lesser parts for $175.
But they say the drive train is 75% used up.
A new drive train (chain and rear cassette) approx $200.
Should I maintain or replace?
I'm a casual rider of perhaps 500 miles a season.

If you're on a budget then keep riding it.

Once the drivetrain is totally shot, the chain will skip on the rear cassette under load, usually up a hill or off a standing start. The options aren't "maintain or replace". It's "ride more or replace".

If you intend to keep it, repalace, as if you don't replace worn parts, they will affect others, leading to an increaced repair cost. Don't understand what you mean by 'maintain' as when a part is worn, it has to be replaced.

For the prices quoted, they seem high, as this is a mechanics forum, can you do any work yourself, as just looking at nashbar, you can get a cassette (5600) and chain for less than $100

I agree the price quoted for a chain and cassette are too high unless the shop is planning on Dura Ace level parts. As jimc101 noted, you can get a perfectly serviceable set for $100 or less.

That said, unless you have really abused your bike and given the chain absolutely no lube or care, 1500 miles (3 years at 500 miles/year) should not have worn those parts to anywhere near the replacement point. I typically get 6000 - 8000 miles on a 10-speed Shimano or Campy lower tier (105 and Veloce) cassette and chain and they aren't a total wreck when I replace them. Chainrings last well in excess of 25,000 miles.

My first recommendation is to find a different shop.

So they are telling you a bike with only 1,500 miles on it needs $375 worth of maintenance? Time to shop LBSs or learn to do it yourself.

It is a local bike shop that has a good rep, but perhaps I'll look elsewhere. I was once good with bike repair, but with multigear, I'm a little put off. If it is indeed time for a new cassette and chain, even though I might accomplish it, I lean more toward having an experience person do it. If parts are $100 then they're looking to charge $100 for labor. How much time is involved?

about 15 minutes

If you shop around, you should be able to get a chain and cassette for around $60-$70 which makes labor approximately $130-$140. I also say get another LBS or do it yourself. I also like to know what small parts they are replacing in the $175 service charge. I wouldn't doubt that your getting soaked there also.

thanks all. Guess it's time to dig in.

Measure the chain. 24 links on a new chain are 12" long center to center on the pins. when it measures 12 and 1/16" wear or streach the chain should be replaced. The cogset should last through two or three chains.
Chain life is a function of care and use.

http://draco.nac.uci.edu/rbfaq/FAQ/8d.2.html

Think chain + cassette + new chainrings..
1500 miles with grungy dry chain could shorten the wear-lifespan..
clean and oiled chain always advised.