I go a step beyond monty and sandman in this discussion. Figure out where you're going to be doing most of your detecting (and for what) first. Are you nugget hunting? Hitting the beach for coins and jewelery? looking for relics? etc. Once you narrow that down, look for the better machines in that category.
Sandman will swear by the Excalibur in the water (and he's right). I agree with that. I swear by the White's DFX on the dry land. Pick the machine you WANT, and get that one. Get the Best machine available. Save your money for the extra week or month it will take to get it. There is nothing worse than getting a machine (or any tool for that matter) because it is "the one you can afford", and then finding out that it won't do what you want/need it to.
If you get a machine that isn't what you want, 1 of 2 things will happen. First thing is wou will get discouraged and give up the hobby, and your machine will sit in the closet unused and forgotten. or second, you'll discover that you should have shelled out the extra 200 bucks in the first place, and you'll end up buying it anyway.
The first detector I bought was "the one I could afford". It is the White's Surfmaster PI. It is a great machine and I still use it occasionally. If i knew then what I knew now, I would have saved the extra 250 and bought the Excalibur (which I ended up getting anyway).
figure out what you want, and get it. you'll be happier, and, the best part... it will pay for itself - many times over
steve