You can clean mineral scale build up with a good vinegar solution if you don't want to use distilled water. Don't use one of those powerful lime scale removers like Lime Away. I don't know that that would do to the tank. Vinegar does a great job. Just like cleaning out the coffee pot.
To minimize build up dump the tank every morning and do a quick rinse out and dry.
Amount of mineral build up and how quick will depend on the mineral content of your tap water. If you live in a hard water area it will build up faster than if your mineral content is lower.
You can always give it a try and if it doesn't build up much and doesn't take much vinegar soaking then it may be an acceptable alternative for you. You can also replace the tank much more often.
You can guy a lot of distilled water for what one tank costs though. If it more for convenience though...it might be worth it too you.