Signature used to have a list of installers, perhaps they have a current one. Roof vs ground mount? I have a metal out building and not messing with the house's composite shingles. Metal roof mounts for ~34 panels $1200-$1400. Those with ground mounts can better estimate that cost. Roof wiring cost probably less unless the ground mount is close to the inverter.
Q1 If just mounting one panel on roof or ground cost more than the panel ...
Other than friends and family you will pay installation labor. Which leads to Q2, balancing quality and cost. It is a normal thing, get estimates and have them itemized. How far off are the panel costs from what you can buy? Hot summers, tax credits, grid issues have made for busy installers, just like the HVAC who want to focus on the most profitable work.
If you are comfortable with wiring, I have seen roofing companies claiming to do solar. They are used to roofs, able to get heavy loads that high, and experienced at avoiding leaks. My shingles were replaced a few years ago and they used a harbor freight winch to pull a sled, holding a square of shingles, up a ladder. Beats asking the wife to lift a 50lb panel high enough for you to pull up.
Looking at my neighbor's install mentioned prior, panels used show online $160 more than Signature equal wattage (different brand). Don't know if the neighbors got a discount or a surcharge but, based on that online price, panels came to almost half of the total cost. But they are happy, $700 electrical bills shrink and the tax credit is a big help for them. They estimate 7.5 year payoff but they are kids, only in their 40s, and can wait.
Lastly, I asked a retired neighbor/contractor, about lower price, lower watts panels vs. more spending more for fewer higher watt panels. He said the usual 'panels are cheap' then added 'but labor is expensive, go big'.