Maybe go for the interview anyway, just for the experience?
Talk to someone else in the department to get an idea of what sort of support is available, ie course books, previous materials (what was the previous teacher doing - can you talk to her/him?).
All the teaching jobs I have ever done have worked out as under the minimum wage. At the moment, I am teaching at a university for about £3.00 an hour, if you take all the materials development, lesson planning, marking, tutorials, emailing students etc into consideration - we all do it.
It's a huge problem. No university could afford to pay us for what we actually do. (However, we do get holiday pay (35 days a year), sick pay, a pension and a certain amount of job security). In your case, it's a temporary cover, so on the plus side, you get to know another institution and might find more work there (if you want it) in the future. On the negative side it would be hard work, but only for a few weeks. Presumably, once you have written the course, you would only have to adapt it for future use there or elsewhere.
If you enjoy teaching and find it rewarding and challenging, as I do, I would go for it.
The agoraphobia, however, is another matter. If it is bad enough to stop you doing any job, then don't go for this one. If you think you could handle it, why not at least go for the interview?
Good luck (whatever you decide).