The lower matters a lot less than the upper. All the lower does is pin onto the upper, hold the trigger components and magazine and bear the serial number. You won't notice the difference (performance-wise) between a $100 lower and a more expensive one.
If you're going to skimp, do it on the lower. If you're going to spend bank, do it on the upper.
Ok, sounds good. So since I will start with the lower due to funds, got any suggestions? Stripped + parts kit or complete? Manufacturer?