I'm in the same boat. I'm a student so I work very limited hours. Most of my income comes from breeding and selling fish currently, which isn't very much, so I know it's tough.
I've never heard of malabar dwarfs, but from what I know about puffers, all will go after snails, and if they can't crush them then they'll go for just the meaty parts, so I personally wouldn't risk it even if it does stay that small.
Basically, you're pretty much stuck with using lettuce or handpicking them unless you remove the nerites somewhere else for a while, but even then if you got another fish/snail to eat them you'd have to rehome one or the other after the population is in control unless you set up another permanent tank. At least from everything I've researched about it that's what I understand.
But, as long as you do not overfeed I doubt you'll have a snail takeover in your tank. In my tanks I've only ever seen a couple at a time, and lately haven't seen any, even in the tanks that I don't keep anything that could possibly eat snails.