Paying a professional to level your backyard could cost anything between $1,000 and $2,000, depending on the size of your yard. If you choose to take on the task of leveling an uneven lawn on your lonesome, however, it should cost no more than $500, even if you have to buy or rent new equipment, but is far more likely to be closer to $100 if you are resourceful and make do with DIY landscaping equipment (see below).
In addition to the savings you can make by going at this lawn care alone, the other considerations are the difficulty involved and time. While some of the stages described below require a fair amount of manual effort, for any moderately fit person capable of handling a rake and shovel this should not be prohibitive.