If I had to give up all my habitat tools today and could only keep one and only one for the rest of my life.... My chainsaw...without a doubt is THE most valuable, cost effective, versatile tool a person can use for habitat work. A good saw only costs a couple hundred bucks, will last a lifetime and you can create food and cover for deer with them....what more do you want?
Some virtually free habitat tools....a box of matches (fire) and a shovel, a metal tinned rake and a backpack sprayer and a small hand held broadcaster seeder are all under $50 each and may require some work, but will get the job done on a small scale. With these you can plant and maintain trees and small plots as well.
Habitat tools do not have to be expensive... The lower cost options will require more physical labor or more hands and may keep your projects smaller in nature....but it can be done. You don't have to have an ATV or tractor to do this....it helps....but isn't required. Also consider that many of the best habitat projects you can do are not the "sexy" ones like plotting. The "dirty" projects like planting trees, hinging, TSI, burns and planting native grasses don't get a lot of press....but are still very important.