or buy a 4" component set and then a dedicated 6.5" midbass and have an even cheaper 3-way set that fits your needs.
Alpine SPX-107R with the SPX-17MB add on mdibass. It's a few years old but i see them for sale for cheap, and the passive crossovers that come with them are AWESOME. super flexible for bi-amp with adjustable crossover points and slopes.
power isn't split by some fixed amount, nor will each driver see the full amp rating. music is dynamic. how much power each speaker gets depends on the signal level in the recording at the range of frequency for the driver, the amplifier gain structure, the impedance load seen by the amp at that range of frequencies - for that instant. tweeters are more efficient and since our hearing is more sensitive to high frequencies, less signal level is required in the mix, and less power is required to drive the speakers. midbass and bass requires much higher signal levels and more power to sound as loud.
if you want to mix-n-match drivers- you run active with a processor. if you want an off-the-shelf solution - you buy a comp set.
with the two amps you could run the smaller amp to a standard 4" component set and use the HPF in the amp. Then you could run the midbass on the larger amp, but you need a bandpass crossover, preferably active, and few amps have that feature. so then you need an active crossover in the mix - a doable thing. even a simple electronic 2-way crossover could work. the typical crossover frequency between 4" mid and 6.5" midbass is around 300Hz, depending on the airspace, driver separation, and driver construction. if they are all in the door, and share airspace, the 6.5 will distort the 4".
with a 700Hz crossover point (with your current crossover plan) you would be better suited with a closed back or dome midrange driver.
Eclipse sold an inexpensive 3-way with a 6.5" woofer and dome mid and tweet. Eclipse SC8365
if you want to spend a grand or more on a comp set - have it professionally installed with door pods.