So as it turns out, if you have an existing bag, converting it in to a pannier is a cost-effective solution. Otherwise it’s probably better to just go buy a new one.
Of note, I am using a special bike rack, it uses the skewer instead of rack mount holes, which is important if you have a road bike that is missing these holes. In particular I am using the Axiom Streamliner Road DLX Rack which has worked out very well for me over the past 200 miles or so.
Total cost:
Bag: $22.00 - a Rothco model, I’ve been very impressed with the quality
Mounting hardware: $11.67 – Home Depot
inverted “drunken octopus wants to fight you” robe hooks, ~$3.25 ea
Top mount view, my rack appears to have been bent in shipment, works fine though
Pannier view from top
Side mount, the bag’s side pockets are extra floppy
Attempting to solve the floppy side pocket problem with some cardboard, first functional cargo test from the corner store
Resolved the floppy side pocket problem by tying the ends together with a crude draw string system, solved the heel strike issue I was running in to.
Inside mounting system. Found some “mending brackets” with roughly the same bolt pattern as the hooks, you can’t see it but there’s a second one sandwiched on the other side between the flap and the main bag, it may do a good job of spreading the load, or else it will fail catastrophically on a major road, get tangled in my spokes and kill me, only time will tell.
Not pictured is a piece of wood bracing the bottom corners of the bag apart on the inside, seems to improve stability and keep the corners from rolling in to the spokes of the rear wheels.