Hatsan Flashpup for around $400 if you like bullpups and don't want to be tinkering with it. I love mine. Benjamin marauder is another good choice quite a bit more money but a proven platform. If you want a slug shooter it will cost more mine was $1600 without a scope. And remember you will need an scba tank, not scuba, a hand pump pure misery or a compressor either large or portable. Mine is portable and was $500.