Hi annie333. Welcome to MLMF. Like Mark said, setting a value without seeing it and knowing your local market is a tough call to make. Does it start easily, run well and do a good job of cutting, or is it hard to start, smokes when running and needs belts or blades sharpened? Are you selling it as something that should last it's buyer a good long time, or as parts for somebody to fix the one they already have? It's condition is going to make a difference in the price you should ask, and it's appeal to the buyers looking.
Here's what I do when I want to sell a piece of lawn care equipment.
Perhaps the best gage to go by is your local Craig's List. Take a look and check for similar ones and sort of go by that.
Also, think in terms of what your guide lines would be if you were looking for one yourself. If there were two identical ones side by side, one all cleaned up, no apparent leaks or issues, and the other dirty and grungy, which would you want? Not that you should have to make it pristine, but a little elbow grease, maybe even a little wax on the hood, goes a long way toward selling what you've got.
Write it up. You don't have to go overboard, but describe it in simple terms, and be honest. If you are selling it as one that the buyer can use as soon as they get it home, mentioning such things in your listing such as New Spark Plug, Oil and Air Filter. Sharp blades, Full tank of gas ready to go...those sort of things are relatively inexpensive, but tend to show care has been taken, and it's something the potential buyer won't have to do right away themselves.
Don't know if you'd consider this sort of thing, but I even offer to deliver stuff up to 10 miles from my house if the buyer doesn't have a truck or doesn't want to carry it in their car. Of course, my wiggle room on the price goes down if they want it delivered, but it has been the selling point for a couple of things I've sold.
Finally, if you are going to sell it through Craig's List, or an online listing that a local newspaper like I have available where I live, pictures are worth a thousand words. CL lets you post up to 4, so show it from the best angles you can, and take pictures on a nice sunny day. If I'm selling a mower, I'll set it in my yard after mowing the grass in front of my wife's flower garden. If it's a snow blower, I set it in my freshly cleared driveway with a pile of snow in the background. That sort of stuff. Hey, think of how car manufactures sell their merchandise!
I know that didn't answer your question of value, but hopefully I gave you some help in raising it's value.