To buy a SaaS company, you often comb through hundreds (if not thousands) of listings from acquisition marketplaces. Here's a list of the acquisition marketplaces, what they're good for, and how best to use them.
Knowing what you want out of an acquisition is half the battle. If you're just looking to acquire cashflow, then the answer is easy: no. Don't buy anything with $0 in revenue because you're in the business of buying revenue!
How much money does it take to start acquiring companies? A lot less than you might think. Try with a $5k maximum and get your feet wet before getting into bigger deals.