A decent local mower shop will probably charge you $3.00-$4.00 to sharpen and balance your blade. A bench grinder works best, and it is easier to show you how to grind your blade than tell you. Most people go wrong by grinding a bit, then looking at their edge, then grinding some more, looking, grinding, and they end up with a rounded edge.
Using the tool rest, keep moving the blade back and forth until the sparks just roll over the back side of the blade. When the sparks do this all of the way across the edge, sharpen the other side. In a fashion, you are duplicating the sharpening of a knife blade (kind of shaving the grinder wheel). Done correctly, you will end up with a nice hollow ground edge. It is worth the time to learn to do this correctly, so take the time to practice.
I know you said you don't have a bench grinder, but a fair one can be purchased pretty cheap these days. I think Home Despot sells Back and Decker bench grinders for ~$30.00 or so. The tool rest is usually a bit short for the whole length of the sharpened edge of the blade, so if you have a buddy that welds, have him weld you up a longer rest. FWIW, this job can make quite a bit of grinder dust, so plan accordingly.