In regards to using cheaper racks with lower weight limits, think hard about what you want to do with the bike. I personally appreciate the better build of a Tubus or one of the other "better" racks. Even when using for errands the higher weight capacity can be a plus. A heavy load of groceries can be a bit much on a cheap rack. I have also carried full propane tanks on my bike and with that weight on top of the rack, a good quality rack makes a difference.