Have any kids around? They can work cheap. Its a very simple job.
Seriously, a rototiller would be simpler. Loosen it up, deep as you can, at lease 8".
This really depends on how big the bumps are and what you plan on doing with the space.
The easy way to dig is with a long handled spading fork. I do it with my shovel too. Just step on it to get the tines deep and pull back on the handle. It loosens the soil and breaks up clods. No reason to lift the dirt and wearout your back. Then rake it smooth.
They make large soil forks just to do this. They go deep (like 18") and you just step and lean. In Territorial Seed company cataloge they are called "Garden Diggers". I would think you may be able to rent one. www.territorialseed.com
One thing I have found that makes raking easier is to put a brick or two on top of the rake. Then you can drag it around and the soil will not lift the tines out of the soil. Not really 'easy' but much better than raking like most people do.
Use a leveling rake, at least 2 feet wide (3 or 4 is better) or you will get lots of ridges and grooves.
You could also get a board, like a 2X6 and ties a rope to each end. It sounds much harder than it ends up being. And the sweat you put into the soil will make the garden even sweeter for you later. You will know what it took to grow you plants. Very satisfying.
OR: Have a dog party. Invite all the neighborhood dogs over and let them run around like crazy! It will loosen up the bumps and then you can rake it smooth. (Oh and clean up the 'piles'. lol)