Welcome to the forum.
There are many choices in metal detectors, I believe most of the $ 300 - $ 400 (Garrett ACE 250, priced less and is a good machine) dollar range will work well for what you want. Some people shy away from used detectors, but if your purchase a brand name that stands behind their products, I see no problem. If possible, try the machine out before the purchasing. If possible, save a bit more and purchase a mid-range detector that has more flexibility. One suggestion, the Garrett AT Pro since it has multi user modes, fairly rugged, waterproof (10 ft.) and a smaller learning curve compared to other quality brands. If you purchase from the dealers on the forum, perhaps a better deal could be realized. Remember you will need a digging tool, pin pointer, finds bag and extra batteries...etc. These will increase the overall cost. This is why a package deal may be a better value if you save a bit more. I hope whatever path chosen will bring you great enjoyment.
Regards,