If you are lucky enough to have access to a beach with happy shells, gather a small variety (leave some for the sea!) and bring them home for a rinse. While I do live near the sea I picked my shells up from a nifty shell shop that I simultaneously adore and abhor (it's complicated, isn't it?) These set me back a smidge shy of $3.
Use strong button magnets which can be found at your local craft store or online, and super strong glue such as E-6000 (also from your local craft store and/or online). Dollop away and allow to cure.
Gift in a happy tin or small fabric bag or keep for yourself and enjoy!