You can most likely get similarly close with the suggestions given using the top mounted tweeter from the DINAS, the HIVI TN28-B. You won’t get the same power handling, but the overall response could be close.
You could go either ported or sealed. It looks like the B&W is sealed, and as far as I can tell from the spec sheet of the linked mid woofer driver (see link above under “Frequently Bought Together”), it calls for a 15L / 0.53CuFt box (no port listed). So a sealed box of that size will give you an F3 of around 46 Hz, but the Qts will be around 0.5, so bass will be tight and fast, but not necessarily super big. (Qts of 0.5 is generally characterized as Jazz-like)
Crossover at about 2600-2700 and that’s where the mid woofer is starting to beam (according to the graphs), and the tweeter is sitting nicely in it’s comfort zone. You may need to pad the tweeter down by a dB or 2, or not, depending on your taste.
In my version of Parts Express, the price for 1 set of drivers (Tweeter/Mid Woofer) comes to about $67, so a pair would be $134 plus whatever the crossover parts would come to along with other materials. Could you do it for under or around $300? Probably, or at least pretty close.
Addendum: Looking at the B&W site, and taking into account 3/4″ box construction, their box volume is 0.575 CuFt, so if you use their outer dimensions with 3/4″ material, that’ll help take into account the mid woofer displacement volume and Crossover volume. Add in a little acousti-stuffing and it seems like a no-brainer. Only thing you’ll have to work out is the crossover.