Rough cost for someone to design and make 2 mid/hi

You need to be careful about specifying 'powerful'.  My 12" drivers are only rated at 450W but given they start out at 101.5dB/1W, power handling isn't everything!

A 2214 loaded with Oberton 12MH35 or B&C 12NDL76 and paired with a half decent 1.4" driver (too many to choose from) would make a lot of noise in a fairly compact box.  Probably as loud as a H3.

 

I don't chase work these days as I'm allways flat out, but happy to build you a pair of cabs to suit your needs..

Whereas the B&C 12NDL76 (nice driver, used them in previous cabs) hits 100dB from 400Hz upwards on the response graphs.  The Oberton 12NMB35 is similar, even though it only quotes 98dB and having played with them are really nice drivers at a non bank-breaking price.

I don't have much experience with RCF compression drivers.  The ND950 looks impressive but I don't really see why you need a 4" VC.  To take advantage of the low extension you'd need a massive horn flare and it would probably be at the expense of some of the top end.  If you want to go RCF then the ND840 would probably be suitable.  However I'd probably go for one of the B&C's or Beyma CP755(ideally Nd version).  The best horn flare I've found and what I use myself is the 18Sound XT1464.

Yes in an ideal world you'd roll some of the high end off the lower 12" but in reality, I don't find it a problem.  If you find it is, then a simple inductor in series to produce a 6dB/oct filter would probably suffice.

The hybrid horn/reflex design Bee is suggestion is an option, however I've tried doing them myself and you do have to cross over really quite low to avoid issues in the upper midrange.  Fine with something like an 8" horn above it but I'm not sure even the BMS will go low enough and to do so would again need a very large waveguide to load it properly.  The XT1464 is pretty big but I still wouldn't take it below about 800Hz. 

Well this is an offer TS cannot refuse!  Perfectly suits your needs