I'd try to find an older big GT with a tiller. I have the best results on garden plots plowing first then tilling. Plows can be found fairly cheap, tillers are usually pricey if they are in good condition. Tilling does a lot better of a job than a disc and harrow ever would. I use an old 1855MF (hydrostatic drive) with over 2600 hrs on it that handles a 48" tiller just fine. With a GT you can usually get a decent mower for it fairly resonable to mow the rest of that property--you said five acres, one and a half for the garden leaves three and a half to mow. I can't see you getting what you really need for anywhere close to $500 but stranger things have happened.