Start small. 1\2 acre is very large without expensive tools. I would go for a tiller, preferably used in very good condition. Using the tiller slowly and carefully will spare it from ruin. And the alternative is paying someone to plow, or a shovel.

Not knowing how big your garden is but knowing that you have 2"-5" rocks, I would go with a rockhound. Here is a video of a rockhound in action.

"Rockhounds"

I see that you are in the same state that I'm in. You know how bad the economy is here. I'll bet that there are 3 to 4 landscapers in your area that are really looking for work. Here is what I would do.

Get at least 2 bids.

Tell them you want to remove rocks to a depth of 6"-8".

Make sure that they are bonded or insured.

And get everything in writing.

This process maybe expensive at first but in the long run you won't be wreaking your equipment and you won't be breaking your back.

Hope this helps.

May your garden feed plenty and your flowers grace the dinner table.

I don't think it would be too much for an old Troy-bilt tiller, but you might want to have somebody turn it over first with a plow.