Hi,
The hard facts are, that an installer has to make money. My system (four panels and a controller), using a factory pre-wire took 8 hours with an installer and a "gopher".
If the seller buys a panel, he marks it up 50%. He *might* get a better deal on the panels than us buying retail--but if he pays $1.00 per watt, he will sell it at $2.00 per watt. The same is true of all the other materials that will be needed.
Add all these costs together, and I think you may find that it costs at least three times more for a "professional" installation than doing it yourself.
Unless you understand what is required for a good installation and insist on it, you may be disappointed with the results.