Some choices for low cost camping on the Baja are Conception Bay south of Mulege and Los Bariles and La Ventana south of La Paz. I have heard good things about Los Angeles Bay on a side road south of Ensenada but have never been there.
Interesting desert camping is at Catavina.
Campgrounds are described in the Church's guide, a must for any Mexican traveler.
I live in Mexico nine months of the year and have r.ved in every Mexican state but two.
You can take all the food into Mexico you want duty free. Liquor is supposed to be one bottle per person but I have had no problems as long as the the amount is reasonable, under ten bottles. Same answer as far as fishing equipment and other sporting goods, clothing, laptops and anything that looks like it belongs in your r.v. including flat screen t.v.'s and sound systems. I have had no problems with my Honda generator. The idea is to get the money spending tourist into Mexico so the Auduana (customs) are reasonable and courteous.
I don't free camp in Mexico. There is very little public land. I camp in campgrounds or where other r.v.'s are parked. If there are r.v.'s parked somewhere, most always there will be some kind of charge. Generally, campground costs are less than in the U.S. but services are usually less.
Roads are rougher and narrower than in the U.S. but have towed my 25 foot safari thousands of miles without damage.
Collision and liability provisions of U.S. insurance are no good in Mexico so Mexican insurance is a must.
I don't fear for my safety in Mexico and have never been the victim of any crime other than petty gas station fraud. There is little road rage in Mexico, it is a different culture. Private handguns are illegal so your chance of getting held up by a punk with a pistol is less than the U.S.
I don't think you save much money by traveling in Mexico. You can park at Quartzite for almost free. You have to go there because you like it and want a new experience or a new adventure and like the food, the culture and the people.