From boat the most typical and basic crab trap used is a box trap
However, for crabbing from shore (I assume you mean piers and docks) box traps typically yield poor results compared to casting traps (not suitable for boat use)
Thats not to say a box won't produce off a dock/pier, just at a slower and more variable rate. A basic 24 inch box trap will run you 30 bucks from Army and Navy, but then you have to factor in a buoy and rope. Army and Navy have 100 feet of lead core plus a buoy on for 21.99 according to their website
http://www.armyandnavy.ca/Pacific-Crabbing-Kit-With-Lead-Core-Rope_p_869.html 100 feet is a bit short for some places as you typically want 20-30 feet of extra line for tides and current, but you can always tie on some extra poly. I would also attach an old boat fender to the marker as they aren't particularly buoyant and it will make your trap stand out from the rest and be more visible. Lots of people just use laundry detergent or milk jugs as buoys, but they are prone to degrading and the DFO has expressed interest in making standardized crab trap buoys a requirement, so may as well get a proper marker. Finally, if you are crabbing in an area with strong currents, additional weight may be necessary to keep the trap anchored, but I have never had this problem crabbing in Indian Arm.