DDR Mom, you dodn't say how often you play or how many people are playing. You don't necessarily need a metal pad. They're expensive, Blueshark is very hard to come by - mymybox only seems to get them in a few times a year and they're gone in a day - and they're $350 + s/h, CF isn't much cheaper. I don't have one, I'm actually using a dense foam "hard" soft mat ignition knockoff I got on ebay that's working pretty darn good - especially for around $30.
I do agree to NOT buy from DDRGame - their stuff is awful. BNS used to be great, but they've lately been completely unresponsive when you contact them and people have been getting different pads than what they ordered. Mymybox does has a dense foam pad for I think $70 - it's a blueshark, just not the huge heavy metal one - I'm thinking about ordering one of those. MMB is another company that is very hard to get hold of though. Just FYI!
On a hardwood floor, if you're using either a soft pad (like the official Konami that comes bundled) or a "hard" soft pad with the dense foam core, you might think about buying one of those rug gripper pads - one of the heavier weight ones. It can help - it won't stop the pad from moving at all, almost nothing will, including the soft pad mod, but it should help.
I really wish Konami/Bemani would come out with official "hard" dense foam mats with the larger sensors/raised arrows and an official metal dance pad with real arcade sensors (like the metal Blueshark has - it wouldn't and COULDN'T be like the one they briefly sold in Japan - that thing was HUGEEEEEEE, but a home-sized metal pad) - I'd much rather deal with Konami and trust their quality control and being able to contact them.