Ajohn, I just reviewed the maintenance schedule provided by motorboater, it doesn't look like there is much more to the service than changing the oil/filter, greasing the main bearing, checking and lubing various parts and possibly replacing the spark plugs.
Changing the oil in both engines shouldn't take more than an hour and most of that time is spent waiting for the oil to be extracted. Greasing, lubing and checking shouldn't take more than 30 minutes, probably less. I replaced my spark plugs the first year I had my boat in less than an hour.
My guess is that this is a 2 to 3 hour job and the cost of materials is around $90'for two gallons of oil and two yamaha oil filters (the latter being $25 each b/c they are yamaha and have a fleece element), spark plugs are another $100 ($12 each for iridiums, possibly 1/2 that for non-iridiums which is what Yamaha provides). If you don't already have the tools and plan to do future maintenance yourself a basic grease gun costs less than $20 and an oil extractor goes for $60 (manual) to $150 (electric) add another $25 for misc. items. In summary labor is $200 to $300 ($100 per hour) and parts should only be another $200 max. So $500 total assuming they replace the plugs with more expensive iridiums which to me means the premium they are charging is about $150. If the are not replacing the plugs they are charging twice as much as they should be.
If you want to bring it in because you have more money than time, I get that but recommend that you take it to the ski clinic in Antioch as Wardial mentioned. You can call them for an estimate first (ask to speak with Tania or Darryl, the owners if possible, Tania usually works the phones) they should be able to give you a quick breakdown of the cost for each service as well as how many days they will need it or the best day to bring it in for a quick turn around. It may actually be closer to your home than Tracy as well.
Alternatively, if you want to do it yourself but are reluctant to without help (at least the first time) call or text me and we can schedule some time to do so, preferably on a Sunday with a start time before 3 (this gives us 3 plus hours of daylight). I have a grease gun and oil extractor so you would only need to get the oil and filters (and plugs if they weren't replaced already and you think you need them, the manual says check them not replace them but once i remove one my practice is to replace it and if I do one I do them all, now that I don't fog the engines I only plan to replace them once every two years). With only 50 hours on the engines I wouldn't even check them, if it were my boat, and it was running well the last time I used it.