Like most things, there is more then one way to go about something. Every person you ask will have different answers. Here are my relevant thoughts to your situation:
When your property has a well and septic on it, you can get away with so much more as far as eccentric building styles. There are ways around having them but they will scrutinize other things more so.
Yes, if you ask someone to quote you prices for those things they will give you general figures, usually higher. Wells are harder to get around as far as doing them yourself or for cheaper, but septics yo can do most of the work yourself. You might need an approved installer to do the final connections or to do a final inspection, but you can certainly dig the field and runs yourself, and probably do most of the work yourself.
The cost of wells is dependent on the depth. If you know you have a good shallow water table then a well couple be as little as $5000.00
It is possible to get away with a composting toilet in some places, but again, they will be a bit more leery of other projects you do.
Power is a tricky one as there are monthly charges associated with having power even if its not being used. Also, if you have a well, naturally you need a ready supply of power. Solar of course is an option, depending on resources. As someone said, you can have a "temporary" power pole set up, as if for a construction site, but the issue with that is it has a time limit on it. If you arent actively constructing they might start to question it. On the other hand, if you do have a building that you are actively constructing, you can probably stretch it for many years.
There must be a way to have a power hook up as if you were going to have a mobile home, i just am not personally familiar with the process and requirements.
Where do you live? Do you know much about local restrictions?