Chris has it right on the bigger parts of the job (like the dike). I rented a backhoe a couple of years ago for $150/4 hours. But I had a truck/trailer and only 5 miles to run it to. It was fun and easy to run. But all I did was put in 40' of culvert. And the Operating Engineers union weren't exactly quacking in there boots over loosing work.
There are a couple of middle buster/subsoiler combinations out there. I had a cheap one (as Chris also suggested) and then later added a middle buster blade. Like someone else noted, use the subsoiler to do the initial break up, then change out the blades (you could buy on of each and then just swap them back and forth).
Long term, I bought a swinging rear blade. If the ground is soft enough I can create a ditch, but keeping in mind that there is no down pressure on a 3 point hitch, you can only dig so much with one. And I am not sure you want too much pressure on your hitch arm anyhow (imbalanced load). The plus side is it's a great maintenance tool for the road, finish work and cleaning out the ditches.
Watch at auctions, local Thrifty Nickle and Craigslist for them. As long as the blade is straight (or the arm on a subsoiler/middle buster) you can fix the rest. My blade had a bad tilt pin (someone broke the pivot assembly quick release pin and replaced it with a bolt -- not convenient).
Examples:
RHINO | Landscape/Construction | Blades | Utility Rear Blades
Sometimes also known as 'potato plows':
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