There are a number of drivers out there that would all be excellent choices, at a number of price points and with a number of different cone materials.
The first place to look, in my opinion, for great performance at a low price would be the Dayton Reference line, the RS125 is a very capable driver if you don't mind the metal cone and are good at xover work.
As P10 mentions above, you've also got the entire 4" HDS range from Peerless. These come in a variety of cone materials, glass fibre, aluminium, coated paper and poly. All of these come with decent motors that include shorting rings and have their own benefits and drawbacks.
Next to the Peerless HDS range you've got the Peerless NE/Platinum line, these used to be the Vifa NE line and are still listed as such at a variety of vendors. These posses very nice motors and reasonably well designed cones. I don't think I've read one person say anything bad about them except that as the cones have some resonance/breakup issues, they could be harder to work with than other soft cone drivers.
Other contenders would be the L12, CA12, W12 drivers from SEAS, although these don't quite offer the same price/performance of some of the other drivers already mentioned. The motors of the L12 and the CA12 aren't up to the standard of the other drivers I've mentioned, the W12 is, but it is very expensive for what you get.
From my point of view what this basically boils down to is how capable you are with regards to designing crossovers. If you've got the ability to control any of the drivers here then I would first go with the RS125 if you need something inexpensive. If you'd rather spend a little more then I would personally go with the 4" from the NE line.