It depends where you live if you live in the southwest then you have a great chance that between government and electric company rebates you can do it totally free
You should install a system that is Certified so it can be hooked to the electric grid this means buying the right parts, saving reciepts and having it inspected. It may also mean you pay someone to install it or at least hook it to your Service line.
Non-certified systems are fine for people that want to live off grid but selling back to the grid during the day means you get that electric back in the evenings when you are home for free and you don’t need as much battery backup.
To Find Rebates this is a great place to start.
http://www.dsireusa.org/
Almost every state has some type of energy rebate program along with the Federal rebate programs
Although any electrician can install electric PV panels and any plumber can install a solar hot water heater you should go to a company that does this as their main business and ask them about designing a system for you.
You will need to know how many panels are needed for the number of people living in your house. You will also need to know about your angle to the sun and available light due to trees, buildings, expected cloudy days and so on.
For this reason you may have to tilt the panels with footings on your roof to get the best light or you may need to add a few extra panels to supplement your specific needs.
You may even need to build up the framing in your roof to support the panels.
Reduce Your Need
You should also think about upgrading other items in your home to reduce your energy consumption. Obviously you will install all compact florescent lights but you may want to upgrade your refrigerator and even your heating system. You will increase your insulation and maybe change windows to insulated versions.
Home inspectors can inspect your house and give you details on what you should upgrade or change to get the best conservation. You can also do much of the work yourself. Finding air leaks in your home is as simple as placing a large box fan in one of your windows. Closing all other windows and doors and using a incense punk near any electrical outlet window or door and look for air flow then fix the problem with caulk, weatherstrip or gaskets.
Try to work with your utilities many of them want to buy your energy credits to offset their coal fire plants and they are meaningless to you other then that they can be barterd with to help pay for your system. Remember all electric companies are required to buy your surplus electricity if your system meets certification so build it right.
If you are smart enough to think about alternative energy then take it the next step and do it as cheap as you can by planing and getting those rebates.