do your self a favor don't go too cheap - you'll be regretting it- but if you find an ace350/250 for that price snatch it up. used you might find one on craigslist or EBAY. but just a suggestion contact Mike Post first and just talk to him before you buy anything, he's knowledgeable and has the best service and deals around.
I just picked up a AT-Pro from him and last summer got my Minelab Etrac from him.
My 13 year old son has a Garrett 550GTAx and a Bounty Hunter Tracker lV. He has been detecting since he was 6. He prefers using his Tracker (you can buy them for $99) and finds some decent coins and relics with it.....even silver.