No speaker designs suggested thus far comes close to meeting that criterion. That doesn't mean they're "bad" speakers, just designed to a different taste that I do not prefer. Only your ears can tell you what sounds good to you.
That's odd,
The guy asked for a speaker KIT priced between 250 and 300 bucks, he has never built a speaker before but has a few buddies to help. The answer provided was for many, many speaker kits from DIY Sound Group...if you looked at them, there are dozens of kits that would work.
Co-axials, concentrics, dome/woofer 2-ways, 2 and 3-way speakers with horns etc. Multiple designers were involved in making the kits be they several Dayton 4" woofers and dome tweeter all the way up to dual 18" 3-way monsters for home theater in a barn.
Think about the speaker he is asking for....a very, very specific speaker if there ever was one. It's tough to recommend a center to a person when you don't know what their mains are etc. I always default to very efficient speakers as it is easy to turn them down but an inefficient center can't be turned up to match a pair of Klipsch Heresy speakers. The guy is running an AVR so the efficiency will help keep all the channels fed properly.
The guy has never built a speaker before, wants a kit at a specific price and it would be good to have people answer questions or provide guidance during his build. The DIY SG stuff is a great place to start, they have their own forum, videos and plenty of people to provide answers to any question he may have. Heck, he can get the crossovers built for him if need be so no fear of screwing up what to most people is rather confusing.
I built my first clean sheet speaker 6 years ago--it was a center channel. Basically, a 2.5 way with XO's at 550Hz and 1.85 KHz with a monster 30mm dome tweeter and four 5.25" mid-woofers. Quite a few of my friends love the ability to hear the spoken word and wanted one...I know the compromises it took to cram all that in a limited space to fit inside existing furniture. Told them it is a custom built one off and the mid-woofers are out of production.
One of the problems with people building speakers be it car audio, PA systems, home speakers or cinema speakers is it's harder to do that it seems on the surface. It is best to start with a kit, watch videos, do some reading and ask all the questions before starting. Having the availability of a flatpack and pre-done boards removes the guess work and should help ensure you don't fry your electronics from making errors.
If you really want options, go to a forum called DIY Audio.... everything from build your own amps to reverse engineering Synergy horns and playing around with electrostatics and full range back loaded horns.
Here is another option if you like traditional MTM type centers with dome tweeters.
http://www.diysoundgroup.com/speaker-kits/denham/denham-kit.html
$197 including the baffle board for mounting the drivers but you'll have to build the box yourself.
Gotta start somewhere and a kit is the best way to get your feet wet. Never know, you might be building some pretty crazy stuff in the future so beware of falling down the rabbit hole.