Hi Mpetersen
welcome to the forum and great question. A couple of questions for you: where do you live (generally) and where do you want to detect - like salt beaches, freshwater lakes and rivers, do you need a waterproof detector or just a dry land detector? Those factors make a big difference. There aren't any waterproof detectors (until the Simplex is released) under $300 unless you can find a slightly used Fisher F44 or a very used one of the Garrett AT series.
For normal (not highly mineralized soil) dry land/dry sand at the beach use along with some shallow fresh water shoreline hunting with just the coil submerged a bit, the Garrett Ace series, Fisher F22, the Teknetics Ameritek Minuteman (same as the Eurotek Pro but less expensive for some reason) and the Whites Treasuremaster will do fine.
good luck,
Jeff