Drill mode's cool, and it's a pity that it isn't in 7th or 8th, but the songlists in 7th or 8th easily make up for it.
As far as controller prices, I don't know. Konami just released a re-made Pop'n Standard controller, and at Play Asia you could buy Pop'n 10 + controller for $100! Don't know if that's still going on. Fine controller, too, with no sticking or anything to worry about. If only they'd give the IIDX standard controller that treatment.
That's another thing about starting with IIDX. Know this: Your keys will stick at one point. Keep 'em clean. You'll need to open up the controller to do so, but it's very, very harmless. There are also modifications you can do to it to fight off the sticking, but I haven't seen anything perfect yet.