This is what I carry in our RV. I don't know if this is "cheap" one or a "good" one - haven't had to really stress it much. This is a two stage bottle jack to provide a good high lift, just in case. It's also way over-kill on tonnage for extra reliability and safety:
http://www.northerntool.com/shop/tools/product_200305495_200305495If I ever have to jack up one corner of our 11,800 lb. Class C RV, I'll jack it a bit too high and put wooden blocks under that corner's suspension components ... and then let the jack back down a bit to put the vehicle's weight onto the blocks (but still keeping the jack in it's hold mode for additional insurance) before crawling under it. Even then I'd try to absolutely minimize how much of my body was under it and how long I was under it. I don't trust jack stands to not twist/tip sideways if one or two of their legs should start to sink into the surface ... 2X6 18 inch long wooden blocks seem to me to be way safer. I carry several of these type of blocks along anyway for leveling.