The Monaco Executive is the 2nd in the line behind the Signature. It is a desirable coach depending on condition and model. Does it have any slides, length, floor plan.
Here is a link to download brochure to you know what you have
https://www.monacocoach.com/service-and-repairs/
You have an option to sell it as is where is but you won't get much for it, there is a 2002 Executive on RVTRADER now for $16500.
If yours in decent running condition I'd think ~$30-50K if it is a desirable floor plan and power plant. These coaches are well built.
If you can get the engine running it will add $$$ to the value. If the rest of it has been maintained that's even better. Sitting that long it could have Algae in the fuel and the filters stopped up. Easiest thing to do is put new filters in and a 5 gallon fuel supply to the primary filter and see if it will start. Check the filters you pull out, algae will be black slime, I had it once and it almost choked off the fuel filter. It there is algae you'll have to have the fuel pumped out and tank cleaned and/or do a fuel polishing routine on the tank.
You probably have 8 tires if it has a tag axle. Rule of thumb is 7 years. I paid $600/tire 4 years ago, these were Yokohama's. I wouldn't go with Michelin due to cost. So your looking at $4800 for tires. So if you don't replace a potential buyer will know this and use it as a negotiation point.
A lot will depend on overall condition, including the roof so if hasn't been maintained that will bring the price down. If there are any signs of leaks on the inside that will hurt. Source of roof leaks are any openings, lap sealant is used to seal so if it is cracked bad it can leak. The roof is a fiberglass roof, I've used a low pressure power washer to clean mine and then painted with Rustoleum top side paint, cost ~$60. It will look good.