Hello bowlersp and welcome. I"m new here myself and your post caught my eye.
Are you a younger guy ? Don't have much in the way of tools ?
What I'd say to the guy who wants to so generously charge you $100 dollars is to just forget it. If you'll round up a few tools from a discount store you can get 95% of the work done by youself in less than two hours. Please don't rush it.
The experience you gain will be worth 10 times the $100 dollars to hire the job done. I'm assuming you have all the parts new in the kit with the instructions. I figure the mechanic who wants $100 for the job won't return the instructions or parts sheet. (this is something you learn with experience)
On the bicycle you are using, you have a choice to just take the handlebar brakes etc apart and turning them over so they look upright or just buying a
used set of upright bars off a scrap bike. You may want to get a larger upright seat that looks like a tractor seat also. If you reuse the handlebars
just put the hand brakes back on it and you can mount your throttle lever and kill switch (if your's has a kill switch to turn the motor off with)
I'd suggest you sit down and read thru the instructions several times and imagine doing the job step by step. The instruction booklet may explain to you just which tools you'll need for each step. But accomplishing a task like this is a rite of passage. What you can do with the bike motor kit can translate to working on a car or lawnmower etc.
Perhaps there will be someone in your neighborhood who would sit with you when you undertake installing it just to have an extra pair of hands around.
I doubt they would want to charge you $100 dollars either.
Most people who haven't done jobs like this before are a bit put off by them.
But believe me knowing you fixed it up yourself once you're riding it will give you a shot of self confidence that's priceless. Remember too there are books in the public library that detail working on bicycles and motors. I doubt you'll have to spend $15 dollars on tools either. When you start riding it stop every
so often and inspect all the bolted connections to make sure everything is holding tight. If not tighten it again and always keep an eye on your work. Don't assume that because you put it together it stay tight forever. Inspect it often.
Good luck and have fun !