the cheapest/best solution is the front lip
http://www.ebay.com/itm/07-08-09-10-...046166&vxp=mtr
ive seen em cheaper, so dont buy from there.
i recently did a repair on an m3 bumper that was cracked, i have some pics (im almost done, just needs the paint). The shop can use this stuff from 3m, or evercoat multifix 2 part epoxy, or plastic weld it together. Then it needs to be painted/cleared. It wont be cheap. And after all that if u tap something when parking it might crack again in the same spot. So you are better off covering it with the lip or get yerself a new bumper, m3 or something nicer.