Thanks for the feedback guys, and appreciate the offer @labs23, I will keep that in mind. The isobaric design looks pretty cool, I had heard/seen a few push/pull designs on my travels; might be an area for future experimentation.

I would have gone down the Mini-Marty route, since the design seems pretty straight forward, but needing an 18" driver, which I estimate would be around $600-800 landed here, plus explaining away the giant boxes in the living room, makes it a non-starter at this time. Maybe at the next house!

I was only going with the 15" over the 12" due to the fact it is only $20 USD more from Parts Express + $28 NZD more in shipping according to YouShop ($95 vs $123). And then get another one in future as funds allow. But reading some of the specs on the 12", I see I will probably need to go to a much bigger box than WAF will allow to make use of the 15", so as you guys have said, I can probably just go for a 12" ported design. According to PE's modelling/recommendations, it looks like a 5.58 cu ft box vented box with a slot/port tuned to 20hz is good for output into the teens.

Also @labs23, did you just buy some MDF sheets and cut it out yourself? I was thinking of trying to get them CNC cut, but doesn't seem to be a whole lot of outfits down here that do them.

I was thinking of getting some vinyl wrap and having a go at that first, and then if that fails, paint it black haha.

Really if I can get the driver landed here for $400 NZD, build a box for less than $200, and amp for $800 (which will be good for a 2 of them), then I'd be hitting around about 2 of them for the price of one PB2000 with equivalent specs (as long as I don't shank it up).