
Best thing to do is get a map and see where the railway lines run, pick a village near the line or statoin and have a look on www.upmystreet.co.uk to get an idea of what the area is like.
Truro is central so you can go North coast, Newquay is the big town there, not well regarded by any one living in Cornwall, South coast, Falmouth there, got all thew amenities but a a bit expensive. Then you could have a look on down round Redruth way, some nice villages out side Redruth and quite a bit cheaper.
There are beaches with in easy driving distance where ever you are in Cornwall, but the down side of this is we have the highest water bills in the UK, all those miles of beaches have to be maintained for the benefit of the tourists who flock here in the summer.
Many beaches are also closed to dogs form Easter to October, again for the benefit of the tourists.