if boss is expensive, iam afraid that your choice will be limited to few things...
anyway, ab selector, go check with ty music center. Someone gave the number in your other thread on the pedalboard. Call them and check what they have or customise one to your spec
And loop pedal, you will have to be specific as in what sort of loop pedal. An A/B selector is actually a loop pedal as well. The same name can be use on a phrase sampler like the boss rc2, rc20, digitech jamman etc.
Both are different and price difference can be really wide. So be specific, if not, there wont be much people replying to the thread..