Affordable security nuts and bolts
If you can find some ball bearings that just fit into the allen key sockets, then you lube them up with thick grease, it's quite difficult to remove them. Use a magnet to get them out.  Although I imagine a good bike thief would carry a magnet because this trick is quite common.  You can also replace your quick release skewers with allen key skewers.  They wouldn't be the most secure solution, but they would work better than quick release skewers.

If you use nutted wheels, you can pick up some security nuts for a lot cheaper than you can buy security skewers. Check you local professional tool supply store and you can probably buy them by the piece for a couple bucks each.

They also sell security skewers which are cheaper than pitlock. The disadvantage over pitlock is that they all use the same specialized tool to remove whereas pitlock has 256 differently shaped pits available.  So they would be safer than quick release, allen key or hex nut, but less so that pitlock.  And almost definitely safer than the bike next to yours.