Heres a quick little guide to make an incredibly easy bump hammer with some local hardware store supplies. I've even found this one to be a bit more reliable compared to the one off of lockpickshop.com. This hammer requires no cutting, measuring, etc, so hopefully it should be easy enough for everyone.
Guide
Alright first step... go to the local hardware store. Here's a little inventory list with pictures to show you what to look for.
Rubber mallet - shouldn't cost more than $1
I don't know the exact name for this rubber thing, but I'll let you know if I do. Mines about 2" by 1" by 1", but it shouldn't matter if its a little bigger or smaller. If you want you can cut off the metal edge using a hacksaw, but this is not necessary if you don't have the tools


Bolt - again should just be some pocket change
Find one of the longer bolts to give you more leverage and make sure it fits into the threading on the mallet.

Electrical Tape - almost free
Now we can give the hammer a nice grip to feel good in the hands

And there we have it, an amazing bump hammer costing no more than a couple bucks and extremely easy to make. Let me know if you have any questions or need some help.
-BZ