Small vs big user studies (and making lots of changes)
Jakob Nielsen points out that more testers result in diminishing returns. The key is acting on feedback from a small number of users regularly.
So, the good news: You can do a few kiosk tests and get really useful feedback. This is cheap, quick and relatively easy to do properly (although asking well-phrased, appropriate questions, setting the right mood and knowing when to keep quiet are skills that take some practice.)
The difficult bit: You need to test a few people often and act on your test results. Doing can be difficult, especially when you’re not the person developing software. In fact, I’d say finding out how much testing and doing any contractor really does should be a central part of any request for proposal and tender process.