The usual advice for mixing sodium hydroxide solutions is to do it in
heat-resistant containers (Pyrex, say). That said, I'm sure it could be
done in plastic if you were mixing sufficiently small quantities of sodium
hydroxide to sufficiently large and cold quantities of water. I'd
recommend not trying, though; Pyrex containers are relatively inexpensive
and easy to obtain. If you must use the plastic container, chill the water
to near freezing before you begin, add the sodium hydroxide a little at a
time, and keep close tabs on the temperature. If it begins to rise too
fast or too high, let the solution cool before adding more sodium
hydroxide.

Why the hell do you want to mess with hydroxides?

They're very caustic and dangerous!

Stainless steel or Pyrex only buy a big measuring cup at the *-mart.

Maybe. Depends on the dilution. If you're mixing a high concentration then  
it would probably be a good idea to keep the vessel in a water bath of  
cold water.