Olamic mid tech or Search Ferrum Forge on the exchange here. Those are the two I would consider the most. Olamic's Wayfarer 247 is an awesome knife!!!
My favorite is Ferrum Forge knives for all around EDC knives, more all around quality than just smooth flipper to play with. I found my FFKW Fortis on the exchange here for $325 like new, best 325 I have ever spent on a knife! If you are looking for something super smooth and solid, you could save a few hundred dollars and get a Real Steel Sea Eagle. Reate knives are very good knives, very solid knives. WE, Rike, Kizer knives are good. One of my top 3 favorites for EDC is Jeremy Robertson's El Patron.
You did not give a size preference, but Lionsteel knives have some great offerings. Brous knives, never owned one, but hear good things. Hinderer knives are good.
The above post is correct though, 300-400 is far from high end, especially when you are talking customs midtechs. But if you do some good searching and have a little patience, you can find some great deals!! Good luck man!