Most of the used shipping container sales are in the 2 grand on up area plus delivery , Around here any way. Might be less in your area. Sometimes you can find a no longer road worthy trailer for less but most are soft sided now from what I see on the road - saves weight - little better fuel mileage , maybe. An old RV might have more issues than it's worth most of which are not visible. Depending on your skill set building a shed in the 2-400 sq ft ( think single car garage) area isn't real hard more of an issue is local zoning for any of this. Power isn't that hard either but again depends on skill set. Floor doesn't have to be concrete either for your use, but do take into consideration what kind of bugs ya got around ( termites and the like.) as that will determine what is needed base wise. Old buses or Box trucks another possible source- Roofs usually need some remediation- with RV's its roof and floors. Heat and /or cooling , hard to beat a mini split for a combined single point system.
Random thoughts that might be of use.
