@ Edward - We tried out the Marketo app, but it seems to be catered towards a "check-in" system for leads already in the system. Looks like there's a Lead capture piece, but as you said it's limited. The breaker for us there is that the lead entry screen seems to be meant for a rep entering the info rather than the Lead. (We're trying to find a simple, more "locked down" interface so that Lead's may enter their own info.)
@ Jason - Yes, we think the hardware scanners and specific apps provided by tradeshow venues are outrageously expensive. We've tried a few universal QR code scanners that come with Lead capture apps on different tradeshow badges, but they never seem to work right with these codes, leading us to believe they are formatted for their proprietary scanning system. No wonder they can lock in such expensive prices... just eliminate any competition.
We're still looking around for something. At this point, our main goal is to find app with a simple UI that is Lead facing... QR scanning and even SFDC/MKTO sync are taking a back seat. I'll post our findings, and of course welcome any more responses or suggestions.