The hard part about breeding crab or shrimp (and a lot of other things) is getting them through the larval stage. There has been a lot of research done on this by the aquaculture industry and a Google search on "Crab Larvae" and "Shrimp Larvae" will produce tons of information.
From what I can see, it's probably not feasible to do this as a means of feeding one or even a dozen octopuses or cuttles.
You mentioned in another post that you are in Washington. If, by that, you happen to mean western Washington State, your easiest solution is to visit a suitable beach at low tide and collect a dozen or so purple shore crabs (Hemigrapsus nudus) which are very common here. You could also put out a shrimp pot (in season of course) from a dock and catch a pretty good supply of 'edible' shrimp (Pandalus spp.) in a few hours. If you're keeping a bimac the water temp you're using wouldn't harm the crabs in the time between their introduction to the tank and their introduction to the octopus. The shrimp may be more sensitive to temp but I'm not sure.
If you can't get to the shore then your best bet for live food is to just bite the bulet and buy it from a vendor such as ShrimpStuff: http://www.shrimpstuff.com/
Breeding crabs will be very hard for the average aquarist and shrimp are about as hard. They have a planktonic larval stages and it would take a while to reach the size you would want to use so unless you have the space and time and muney it is not worth it.
Im not sure if you have Mysis shrimp where you are based but they are fairly easy to breed. I'll look out an article for you. There was one in a recent magasine called Marine World which does have some outlets in the USA.
I'll see what I can find. I'd imagine Colin will have done it at some point.... he's a clever chappy