I have the Pioneer A05 which burns at 4x. I have burned DVDs using many different brands of media and have used both DVD-R and DVD-RW. I have played the resulting DVD-R disks on several different set-top DVD players and everything has worked well. The only problems I have had were the result of using several lousy authoring programs (Sonic's "MyDVD" that came with the drive, and Ulead's MovieFactory which I purchased). I experimented with the Vegas/DVD Architect beta, but wasn't allowed to burn anything, so I can't tell you how it works at 4x with this software. However, the point of this post is to say that the hardware itself seems solid.
I have the Sony DRU-500A, and have used it to burn +R, +RW, and -R media. Once I got past Nero's buggy DVD-Video template, every player I've tried has read the DVDs flawlessly. It will burn 4x on +R media, and I *think* it can do 4x on -R media with the right firmware, but don't quote me on that.
However, you said you wanted "a reasonable price", and this burner is more expensive than the Pioneer models at about $340.