I sure like my Lesche digger. $34 to $40 depending where you buy one but they are a good investment. Depending on soil & decorum I use the Lesche, a U.S. Marine Corps fighting knife (70's Camillus version), a stainless steel bulb planter from Lowes with a narrow, half-round blade and a large, cushy hand grip and or a small wood handled trowel that was something my wife got free for a garden book club.
Don't show up at a town park or school with a 7" fighting knife. Bad form.
I also carry a bricklayer's hammer if I'm cellar holing, in the woods, or where there might be fossils. Great for chopping out tree roots, splitting shale, breaking up hardpan, etc. You can spend 2X more and get a chisel head geologist's/rock hammer - same tool.