Your not the first to ask for it, so I guess I'll have to figure it out.
> $10 if it could export UML or some kind of XML definition
Interesting. One of the features I plan to work on this week is export & import of source files. My first plan is to 'brute force' it, and export a .json file with a attributes for each cell in the grid. But could also be yml, or even XML I guess.
I do actually have one in my possession for day-job, but don't want to mix private projects on that laptop.
The reason I mentioned UML/XML are because those are the languages used by most popular wireframing apps for cross compatibility - if you do decide to add that feature, I would look into how they implement it specifically and it will probably save you a lot of work too!
So you don't need a developer account for development. If you use the same icloud account that's on the phone (I use an iPhone SE original edition), you can login to XCode and deploy your app to your phone for 7 days I believe. Great for development.
You're SOL on the Macbook though, ask around, maybe you have a buddy that can loan you one (or get a cheapo used macbook air with a busted display or something)
If it was available on iPad, I'd pay $5 for it personally, $10 if it could export UML or some kind of XML definition.