Well, a PI is next to none in a beach. I belive the Garrett ATX is still in your price range, there is a bunch of military machines in this price range, but check if they provide discrimination, not all do. If you need something cheaper, there is an assembled PCB available named NH-173, a copy of sniffer xr 71, a legendary PI from deep seeking realm but it would perform with 15cm coil with flying coloures, it has none discrimination, but for 60 EUR, you can't conplain. There is another PCB available on the same sit, NH-250, this is a copy of FelezJoo detector with suported discrimination, but you may have to make the discriminator work by yourselfe. The "magic numbers" of the sistem are way off, and you will have to adjust the coil at least. All in all i am a bit dissapointed with FelezJoo, and i do not reccomend it, but than again, for 40 EUR you cannot miss. Once you fix the discrimination it will work on the beach just fine. Then, there is a real king on the beach, in my oppinion, the Miner4, but it takes a skilled hand to be build from the schratch.