Don't buy degreaser. My mother taught me to use Dawn or Palmolive (or a similar dish soap in terms of grease fighting) directly on the stove top or on another area that you want to clean grease off. Just put it on thickly, let it set for about 5 minutes.
A natural and inexpensive degreaser is to keep white vinegar, water, and perhaps a drop of dish detergent in a spray bottle. This is handy to keep in the kitchen, but can be used in any room.
This is a page about super duper de-greaser. Reuse little soap slivers to make an effective all purpose kitchen cleaner.
This is a page about homemade stove degreaser recipes. Cooking usually means that there are grease spatters on your stove.