cost of valve stem seals vs. do-it-yourself on '89 300E?

Have an '89 300E with 160K that is starting to show a little black smoke out the tailpipe when following the wife. Uses @1 qt. of oil every 1,000-1,500 miles. Plugs seem fine.

Just got a quote of $570 for valve seals from a foreign car shop. Seems a little high to me. What price should I expect? Is this a job for a moderate DIY? (For perspective, the last head I changed was on a 1957 Studebaker Hawk! Yes, I know the head doesn't come off for the seals.)

If a shop changes the seals, I assume they will check the guides. Is it usual to have to repalce them at this mileage? If so, I know I don't have the tools for that one!

Thanks!