Depends on how handy you are. I am in the same situation except mine had been sitting idle for perhaps over a year as it was an estate sale. The generator wouldn't start but that turned out to be a collapsed batter which was easy enough to change out. I don't have the generator set to test start and run weekly and have the fuel (LP) turned off. I do notice that when I start it every month or every other month, it will take some cranking to start up. I hook up the battery to a charger every 3 months or so to make sure it has enough charge (it's also a car battery so it ha a lot more cranking amps that the stock battery).
The other thing is oil change. Oil looks good on mine and gas is apparently cleaner than gasoline so it isn't contaminated as fast. I will put i synthetic oil at the next change as that doesn't break down as fast as conventional oil and also clings longer - better for less-frequent starts. I also have to check the air filter.

What's the make and model of the genset? This is big enough so it might be a water-cooled industrial engine. I have little experience except for checking on the one that I arranged to have installed at my dad's house very recently. It is a 16 kW Generac. It is the easiest engine I've ever changed oil on. The filter is simple as well. If it is water-cooled, you need to think about coolant as well, but how hard can that be? Shop around for a service/repair contract if you like, but maint. is pretty easy. The genset that I mentioned does not yet have enough hours for a valve adjustment, but I bought the gaskets to do that when I bought the genset.

I have two problems with the exercise program for the air cooled Generac sets. First, they run the thing at half speed to keep the annoying noise down. I guess they can check the power characteristics at that speed to a certain extent, but without a load, I don't know how far they can really get. I asked the installer, who I know fairly well, why they don't do a transfer with a load test. He shrugged and suggested that maybe people don't like to reset all their clocks. Second problem is that the exercise cycle is not long enough to get the thing sufficiently warmed up to keep the oil free of moisture. I was up there a couple of weeks ago and the oil was milky-looking . I shut the main power off and ran it for an hour and it looked fine the next day. Before the great synthetic oils that we now have, in that climate, the oil would have to be changed twice a year to have the right oil for the ambient temp. Now, it does not have to be done as often.

At the onset of my experience, I would have advised to do a real test at least twice a year when the clocks need attention anyway. Given more recent observations, I'd run it hard at least once a month in the winter months. There were two problems that were on fault of Generac. The first had to do with battery charging that was probably precipitated by the local POCO (NYSEG which according to my limited observations usually does a pretty good job) when they crossed two phases of a main high voltage supply when raising it temporarily over the nearby state hwy to get a very tall steam generator down the road. I understand that a lot of appliances got cooked. I think that my friendly installer came over and reset a breaker for the charge circuit, but whatever it was, it took him minutes. The only other thing was that the gas line got waterlogged. The same guy analyses the problem and called the gas company to fix that. More frequent hard running might have prevented that.

Those prices look stupid high to me unless you are really out in the boondocks a hundred miles from the company and any parts supplies. I feel that way even if it is a service contract that covers repairs rather than just a maint. contract. These things do self-diagnostics and tell you if something is wrong these days although if you have a very old genset, maybe your does not. I'd be looking at getting a service manual and learning how to do routine checks on the operation. I can't imagine that it would be much more than doing a load test checking voltage on both legs and the frequency which is all pretty darned easy. Routine maint, on the prime mover would be oil, filter, coolant, maybe an air filter now and then and a load test on the battery. You'd want to listen to it start up and run, and a valve adjustment might be needed every few thousand hours.