Well that's not true, in ppc traffic sources also you can test with lower budget, but they are expensive compared to pop traffic.
why part time if you don't have a daily job ?.
if you have a daily job al you have to do is this:
set up a test campaign with $10 to $20 budget, and leave it run for the whole day.
then come back the next day and analyse the results, but from time to time you will need to optimise the campaigns sometimes you get lot of traffic sent by some placements with bots and you get charged for it, all you have to do is to pay closer attention to it, that's it.
with pop you will need to optimise each 3 ours or so, especially if your campaigns is still new in the traffic source.