A topic that is often covered here. Specialised toy cases tend to be rather expensive, some people use a suitcase or a laptop case or large vanity case that cna be cheaper and can hold what you need and have different compartments for different types of toy. And you can easily attatch a lock seperately yourself.
I use a large cardboard box that has a nice print on it. Got it for a fiver from a discount shop, and is basically just a storage box for paperwork etc. But it's big enough to fit most of my toys, and nice enough but also discreet enough to have in my cupboard or under the bed, or even on display without anyone going Ooh, whats in here!