How can I keep hobby knives sharp on the cheap? Whetstone? Other?

I'm not a fan of constantly disposing of blades and I find they dull fast working with kitbashing. I mostly use cheap dollarstore x-acto knives or those hobby tool knives that look like a scalpel with a single blade held in its head.

Is my problem that I am using cheap knives? Is there a wonder knife out there that will keep its edge? If no blade will survive, how can I reduce the frequency of dulling? I know whetstones are a thing but I am not familiar with their use outside of kitchen knives.