I've been through this on a few occasions.

Plan A - Talk to your neighboors and agree on a time/day to do drums. If we're talking about Real Rock Drumming on a Real Acoustic Set, the amount of time and money spent soundproofing will not yield a great return IMO, unless you only need a wee bit of high end filtered.

Plan B - Find a nice room somewhere and track your drums there. This can suck if you track daily.

Plan C - Build the room-inside-a-room that provides both mechanical and HVAC isolation. Who needs cash anyway? :w:

Plan D - F*ck 'em, act like a raving Michael Keaton in 'Pacific Heights', intimidate them and create an environment of perpetual fear within your building. They will totally leave you alone.

Note that Plan D has some downsides.

I wouldn't recommend V-Drums to my worst enemies. Or any electronic drums for that matter (again we're talking Rock Band Context here).

In the old days my buddies and I used to do guerilla drum sessions in Chicago. For fun about once a month we'd scope out a nice room, then show up at some off time looking like some official production and setup our gear. Then immediately we'd soundcheck and start tracking to see how long we could go. Eventually some security people would show up and it would end abruptly. But we did drums in the lobby of the Shedd Aquarium, the EL tunnel between Jackson and Madison, the middle of lower Wacker drive tunnel, and a few others.

That was absolutely irrelevant to your question, but it reminded me of some crazy times.

Good luck-