Overnighting in rest areas vary by the State, some have 3 - 6 hour limits, others have 12 -24 hour limits. There are a variety of stores that allow RV parking some are more friendly about it than others, Wal-Mart has a pro RV overnighting corporate policy, but leave the actual decision up the the individual store a mangers, some / many towns have parking laws that don't allow it, again here enforcement varies. There are also generally more peaceful alternatives like Cracker Barrel restaurants, most / all of which have RV parking spaces generally allow overnight parking, I have also heard Cabella's sporting goods encourages it and some even have RV dump stations, in fact they have a full service campground at their corporate headquarters in Sidney, Nebraska.
In addition to free camping there are a lot of low cost camping options out there, particularly in the central part of the US. These include forest service campgrounds, these generally don't have hookups, but may typically have pit toilets and limited fresh water on site, but the price is right at around $10 per night often with great scenery. Dispersed / boondock camping in some of these forest service parks is even cheaper, or free. Many small towns have RV sites in their public parks, at community centers, etc. often available at minimal charge $10-$20, some are even free for the first night or simply ask for a donation in order to keep them free. This is really not bad considering these sites often have water and at least some electricity (20 or 30 amp hookups) as well as often free dump stations on site. Then of course there are COE and State park campground,which vary by location, but are often cheaper than commercial RV parks, with prices for sites with at least electric and water hookups in the $20-$30 ballpark.
