[blueheart]

It seems that my original idea would be quite easy to implement, and would definitely work, but just wouldn't be safe.

If you just wanted something for little cost it's not difficult to put together a homemade setup which would do the job. It's been done before that someone made a pump even including domes for no more than $15. But in your case you want a Brava-Evebra type device which is something else entirely. That's the problem here, that you want something which would work with very low pressure for a long time without you having to operate it.