Most inexpensive I have found are the Moose guards, around $45. You can order them for either small or fat bars. Some brands you have to buy the fat bar mounts for extra $$. The plastic sets aren't a whole lot more if you need them.
I think they aren't as strong as most of the guys here want but at 1/2 the price (or less) they work good for me and my kid. We have abused them good for 2 riding seasons and no complaints.
They are a bit of a hassle to fit though because of the hydraulic hoses. A sturdy vise and strong crescent wrench (or pipe wrench with a rag to not damage the finish) and you can tweak them to fit. If you don't have a vise to "adjust" them I'm not sure you could make them fit.
Our main concern was broken levers (from dropping the bike) and broken hands (from hitting trees).
Do a search because this subject has been covered a hundred times and many members have included photos of some really nice set-ups.