Best $100 spent

Well not even $100 but pretty close once tax and shipping was added. But I just picked up DUI's weight & trim II harness weight system. I always told my self that I'd never pay that much for a fancy weight belt but that changed after only one use. I tried it on my last dive and didn't even realize I was wearing weight until I started to ascend. I wore the waist clip really loose and had the weights a lot lower than normal and I loved it. Also on land it felt like a lot less weight because it's not just on your hips.

So what was your last great purchase that was relatively inexpensive?

What I NEED to get that is inexpensive is thin waterproof dive socks. I really get some wear marks after 4 days of trip diving.

sometimes it's the little cheap things that really help...... but that seems to be pretty rare or at least in diving:)

I have to disagree, some of the cheapest items can be an extremely important and useful part of diving.

Some of the items I can think of off the top of my head:

Batterys
O-Rings
Mask/Fin strap
air fill
dive slate
dive log
safety sausage
save a dive kit
whistle
brass clips
ear drops (ear beer, etc)
mesh bag
fish/critter id guide
jon line
and a towel (Remember Towlie says, "never forget to bring a towel")

ok I mean the convenience factor those are mostly necessitates.