Instead of thinking of a hard number now, or even thinking about the current market prices right now - I would expand a little "outside the box".
First, come up with your list of services and things you would be wanting to do. Then, estimate the logistics of this - how long would it take you to accomplish these things daily/hourly (this will show your investment in time and thinking logistics starts the process of delivering services more efficiently).
Once you know what your investment is - time AND capital - then you can start to think about your customers. Is there any way you can profile these people? Do you know them? If so, what do they do? Can you look up and "average earnings" based upon what they do to estimate income? (point here - try to know as much about your market as possible). What are the airplanes they own worth roughly? How much avarage income does someone in their profession make? Google is your friend - NEVER had this kind of tool when I was a kid.
Keep in mind - people are hiring you not necessarily because they are too lazy or even mind doing stuff like this. The primary reason they would hire you to do this is to save time. I don't really care to have employees at all - it isn't a goal for me to have people work for me or not and generally they are a pain in the ass. The point is though, I can buy their time for less money than I can spend my own, thereby allowing me to use my own time making more money on other tasks than I pay them. The people you are hoping to provide this service for feel the same way (although they may not articulate it). The idea is that they are busy and their time is worth "x" amount of dollars (assume a 2000 hour work year). If they make $200,000 annually, you can roughly estimate that they make $100 per hour (although they certainly work more hours...but you have to start somewhere). The idea is that if they are worth $100 per hour, and you can save them "x" amount of hours per week/month by doing mundane crap then you have created value ("x" amount of hours times "x" dollars per hour). from this you can factor in the value you are creating and price your services as some amount of that figure. If you are asked how you created the pricing you can explain your estimates and that would allow you to explain the economic value as well as time that you are creating for these people.
Having a set methodology for your pricing allows you to decide if this is something that makes economic sense for you, and it also allows you to be able to easily explain it to your clients and prospective clients in order to show the value of your services. Pricing things based only upon the market prices for services in your area smply means that you are cedeing control of your pricing to others, and it also assumes that the services are equivalent - which wouldn't be the case in comparing a simple airplane washing to an "aircraft concierge" service. Sharpen the pencil and do these kinds of thoughts/calculations prior to starting the business/endevor. If it makes sense on paper and you can accomplish your goals faster than simply taking a job at McDonalds, then do it. If fry-man at McDonalds would get you down the road faster, then do that. Either way, come up with this kind of thinking prior to starting - too many people hang out a shingle and start a business with no deeper though than "Hey, it would be cool to have my own business", not understanding if it is actually financially worthwhile or viable prior to doing it.
