I think you can shorten that. It's difficult to find a pannier for a reasonable price. Period.

A rucksack strapped to a bungee cord sounds like something that might just do the trick. I imagine it can be somewhat of a pain though, having to deal with those bungees every time you want to attach the rucksack to, or remove it from, the rack. But if you get skilled at this, it probably takes you mere seconds.