I have used the at pro among other detectors and would recommend it for someone in your case. Its very easy to use gives you a lot of info before digging and is not going to cost you a mortgage payment. It didn't get the depth I expected from an 11" dd coil but it still gets the job done quickly and was still suprisingly pretty good in trash for such a big coil. {Everywhere I go has lots of trash. IE every other swing goes beep beep. Even with iron notched.} I wouldn't spend more than 450 for one used. I just sold mine because I never went in the water with it like I thought I would. I just got a CZ70 pro off craigslist for a few bucks and yeh. I see why CZ's are hard to find PEOPLE HOARD THEM! The guy I bought mine from had a minelab a cz 21 and 2 cz 70 pros. He said it was his backup to his other cz 70 and never used it!
There aren't as many options as you might think when it comes to detecting.
Some people like digital some people like more analog knob setting styles using there ears mainly and then confirming with a screen and VDI. Some people like the option of both or all at once. At the end of the day its what works for you. I haven't met a metal detectorists whos only had one metal detector his/her whole life so I wouldn't try and overthink it too much.
Get something with a good resell value if your nervous or doubtful. Minelabs always sell but I think in the 3 4 5 hundred dollar range your more likely to get most of your money back when reselling as opposed to getting a 1400 dollar machine and only get back 8 or 9 hundred for it when you realize its not the end all be all of metal detectors.
Hope I could help.
Your in the right place. people in this forum actually answer you back when you have questions.