i have the B52 Matrix 1000 system (2x 10" 2way mains + 15"sub) with all ins/outs and power onboard the castered sub. Strap everything onto the sub- how it is intended- and roll!
the 12" 2way mains plus 18"sub "Matrix2000" may work for you, also but doesn't quite fit as comfy in any ole car trunk or backseat
I'll 2nd the Matrix 1000 vote assuming you need DJ level bass on a tight budget.
I'm sure the Matrix 2000 sounds better and gets louder, but it is priced considerably higher than the 1000 and at that level, I think there are better all around competition out there assuming the overall sound quality is similar to the 1000. (but of course with more bass extension and volume)
The downside to the Matrix is, the amp is built into the sub so the tops are passive. If you wanted to use the tops without the sub, you would need to power them with another amp. However, since you have a passive system, that might not be an issue depending on your amp power output. They're also covered in rat fur which I'm not fond of.
If you don't need booming bass, I would look at the EV ZLX, ZXA1 and Live-X lines, picking what you need from each. The ZXA1 powered 8" over ZXA1-SUB 12" sub is impressive for its size from what I've heard. For more bass look at the ELX118P but it still won't get you anything like say SRX718S in any way shape or form.
For an excellent semi-compact sub and very good, versatile tops at a higher price, a pair of K10 over KW181 would be my vote. I believe an external crossover would be required to pull this off, but you already have one of those, right?
The entire Yamaha DXR/DSR lineup is getting rave reviews. Personally, I would only go that way if I were getting a different sub. I wouldn't mind at all, DXR10 or 12 over KW181.
Another consideration is, maybe your small system mains can double as large system monitors? If so, consider that application too. If going powered, consider tops without a crossover output for subs as that adds expense.