I'm not sure I follow this. Are you saying it's OK for her to expect him to host, but not OK for him to expect her to host? Please clarify.
Not sure I'm seeing the difference here either. Why is it OK if it is a couple, but not a single?
If something were to "go wrong" at a guy's house, how important would that $30-$50 seem then?
Looking back through your board activity, it appears you two have been swinging 2 or 3 months now. You've made several references to babysitter issues cutting down on the amount of time you've been able to go out. So, I'm assuming that within those 3 months, you haven't actually been able to play a whole lot yet. So, you're still relatively new to swinging in general.
Many (most?) of the responders to your thread have a lot of years of experience under their belt. These are wise, savvy, and well-reasoned individuals. If any one of them gave me feedback that they felt I needed to take to heart, I would spend a generous amount of time contemplating what they told me, and, most likely, take the advice they've given me, and I'm a pretty stubborn individual at times.
They've given you some very good feedback and advice. Advice that I wouldn't be so quick to brush aside. I would spend some time rethinking the hosting/being hosted thing, regardless of the potential playmate's status.