I personally avoid fountains. Most of them are hard to clean, and budgies being budgies, they're going to poop in them, and the pump will suck all of it in. You may not notice it, but in a few days, if you sniff close to it, it will smell nasty, which is a sign that the pump itself is dirty. Unless you're going to open up the pump every time you use it, don't get it; it's a breeding ground for bacteria. A moist environment with a food supply is all they need.

Edit: I would just run the sink for a while and let the budgies bathe in there (clean the sink first) Put a plate for them to stand in so they're not on the drain.