4500 . . . get a set of V-drums new. As far as I know,
the DTX V2.0 kit only cost 2000-2500 new.
Overall, the DTX V2.0 is a better machine. It has better sounds, more processing power and also has a built in sequencer. The layout of the controls is also much more user friendly.
The DTXpress is an excellent practice unit and may be better suited for your purposes (and cheaper). But, here's a quick comparison. . . .
v2.0 has a polyphony of 32 - xpress has 16
v2.0 has an effects processor - xpress has none
v2.0 has 64 drum kits - xpress has 48
v2.0 has 880 sounds - xpress has 928
v2.0 has a sequencer - xpress has none
I guess the real question is, what kind of triggers are they packaged with? The DTXpress is generally packaged as a standard five piece with rubber pads, while there are a number of different configurations with the DTX V2.0. All the v2.0 kits I've seen use rubber pads as well. Unless the kit was upgraded to mesh pads (and a lot of them) I can hardly see any justification of that price.
Hope that helps.