Pdmoderator;
I'm a professional locksmith. You need to put out a little more information please. What is the largest shackle diameter that will easily fit through your case's retaining hasps? Will the case configuration let you use a guarded hasp type padlock? Do you want keyed or combination? If keyed, do you want key control? Do you have a budget?
Master makes all sizes & types of padlocks, including some quite good ones that you won't see at Wally-world. All-in-all, I'm going to take a flyer, based on experience, & suggest you go to a lock shop & look at the Master 6121. I'd think that it will retail for something in the high 'teens. But I don't know your market, of course. Considering the cost of the contents, that's really not very expensive. Although I'm sure that it's a bit of a shock compared to the typical box store padlock.
The 6121 also has some very useful points to recommend it. It is re-keyable. Therefore if you should think that someone got a key that shouldn't, you don't have to buy new locks. Just get your present ones re-keyed. It also does not have a shackle spring to rust or break. They are rubber armored & have a keyway protector flap.
900F