Not come across them using 2 straws before.
Genus certainly had both a black and belted galloway on their books.
AI can be a bit hit and miss - we get about a 70% hit ratio for the ones we spot bulling. Some cows can have a very short period of heat. Dominant cows tend not to be ridden in my experience, so you need to keep a good eye on them, watch for other signs such as bellowing at the boundaries. We've had cows that we have never managed to get into calf through AI but have with a bull

.
However after saying all that, for a small number of cows it's not worth the hassle and expense of running a bull, and we've stuck with AI despite its drawbacks, and you get some of the best quality sires out there. Cost is about £10/service and the cost of the straw, which can vary from £10 up to over £100 depending on the bull, whether there are royalties etc. I would imagine the galloways would be at the lower end. You could also go for a X with Angus etc if you don't need them to be pedigree, and you'll get a lot more choice.
Regards
Mike