There are several different solar panel designs available.
Monocrystalline solar panels are built from monocrystalline silicon cells. It is the oldest solar cell technology, so it is one of the cheapest available options. Monocrystalline silicon cells don’t have a square shape though, so some of the space is wasted. To produce such cells more energy is required comparing to other designs, thus making it not the best choice if you care about environment.
Polycrystalline silicon cells are also quite cheap and they can be perfectly square allowing to use every inch of available space for power generation. They use less energy during manufacturing and so far offer the best efficiency. Looks like currently it is the best choice on the market.
Amorphous or thin film solar cells require much less energy during manufacturing comparing to two previous designs. They are durable, portable and supposed to be much cheaper. Unfortunately this technology is still quite new and prices are still high on them. Maybe in a ten years or so they will capture the market.
While you can buy a ready panel you can save a bit of money if you build it yourself. It is not very difficult, you can buy solar cells, solder them together and wrap in a frame with plexiglass for example. There are a lot of books available which can show you every step of how to do it. You can even find videos on youtube and save money on book too.
Major benefits of solar panels are of course independence and gas savings (because you don’t have to run your generator). You may ask are solar panels worth it? There is no answer for everybody. I would tell you, that if you have some money to spend and you don’t spend too much electricity and you use your RV quite often and you go to places where there is a lot of sun during the day, then yes, they worth it. Average cost of solar panel could run in about $1-$2 per watt if you make them yourself and probably $5-$10 per watt if you buy them assembled. As you can see you will get best price solar panels if you make them yourself from individual cells.