I like sphere because on its own it's pleasing. I dislike sphere because the secondary hull is usually not blended well and something in my mind says nacelle/warp performance is a little hinky. I don't know which is better narratively seeing results closer to our future configurations at a small scale or seeing the hinkyness for science.
The cost differential at this stage is nothing IMO. Not slapping an extra 2-5 cannons, 2-3 torpedo launchers, or a massive secondary hull requiring odd deflector stuff is where a lot of savings come from.
I'd vote half saucer if we're looking for nimble single-role and full saucer if we're really afraid of space and can deal with some mission creep. Nimble helps dodge asteroids, get away from random awakened tech, get closer to things of interest, but more space could mean we shove in an expanded medbay/transporter bank.
Do medbays, transporters, or future astrogation labs (cargo bays) add cost?