Lights

I've been using 2 of these, each mounted on a twofish lockblock (on the handlebars) for night riding over the last 2 years.

The 1 mode version is best (it wont change modes when you hit bumps). Having 2 lights is good for peace-of-mind if your riding out in the country as a failed light could be a real problem. They are plenty bright enough for group riding and medium paced (20mph ish) stuff. You'll need a bunch of 18650 batteries, a charger and a US socket adapter but it's still within your budget.

I've bought a 900 lumen light now, just for the occasion when I want to ride fast on my own... or get dropped from the group.

:)

This'd be the sensible option but I am tempted by the (no doubt over the top) SSC-P7, with (apparently) 900 lumens and a separate battery pack, but just over budget.