First of all, check your County landfill to see if they have a composting program. Ours has a great one, and the compost is excellent, and free ! ! but you'd need to go get it yourself, or hire someone to fetch it for you. Compost is the 'gold standard' for filling beds and the more of it you get, the better off you will be, and the better your stuff will grow. In Utah, where we amended my daughter's garden with 30 loads of compost, they charge $25 for a pickup truck load, but they will load it for you with their front-end loader.
We've filled raised beds at our school gardens for years with the free compost from our landfill and they've been absolutely amazing. The only down side is you will need to go get more every year or two, because in hot, humid climates all organic material in soil breaks down pretty fast, so the level of your beds will drop as the stuff breaks down and is used up by your plants. The same thing will happen if you pay big bucks and get really good topsoil because it will have a high component of compost in it, too.