You can get speakers that have the tweeters built in, they are called 2 or 3 way speakers. The better ones have external crossovers.
But you dont have to drill holes as most come with adaptors for different installations and may look OK on your dash, mine are stuck on with double sided tape.
I was only suggesting not to buy Hertz as have had a few mates who have also had faulty sets of their cheaper speakers and I had crap service.
I wouldn't call my stereo massivly powerful or competition grade either.
My front splits are rated at 175W RMS and they are getting only 45W RMS so they could handle a lot more!!
It just sounds incredibly clear now and if I bothered to install them properly and sound deaden the doors with bigger amps I would have an amazing stereo.
As far as which brand to buy at your price range, the best thing I could suggest is to try listening to a few speakers in the shop if you can.
This is a really good
guide to follow when buying speakers, I know its advertising but its correct>
You could buy a pair of these
speakers as they are around $200 and are 5X7's and would slot straight in,
There is also a set of Boston Acoustics that are around the $300 mark that sound really nice.