Your vet should be able to get any number of sponges - mine come packed in dog poop bag, I guess that way the vets isn't falling foul of the plastic-bag tax....
Can't find a bill right now, but not that expensive if it reduces your travelling time. (and in my case also results in batch kidding rather than one a week... and going on for ever).
Friend of mine just took her goats to somewhere to be mated after sponging (but she used PMSG) and found that they were still very much in season 48 hours after taking sponges out, so you have a fairly good window to go.
Day 8 or 9 after season should be fine, as long as you are over the 21 day mark for the later goat.