In reply to Rob Laird:
Two buses will get you to Llanberis
Service: 6 - Bangor - BethesdaYsbyty Gwynedd (SW-bound), Grounds, Bangor
From: Spar(NW-bound), High Street, Bethesda
To: Ysbyty Gwynedd (SW-bound), Grounds, Bangor
then
Service: 85 - Llanberis - Bangor
From: Ysbyty Gwynedd (SW-bound), Grounds, Bangor
To: Interchange (SE-bound), A4086, Snowdon Mountain Railway Stn, Llanberis
Stay in Llanberis or get bus upto Pen y Pass then walk up the big hill and start
the slog
The website below should help you plan your itinerary
http://www.traveline.cymru/