Public transport wise there aren't really any good options. Only other service is Bus Feda, but they leave even earlier. Timing of the match means you won't be able to get a bus from Galway to anywhere until next morning unfortunately (would have liked it a bit earlier myself so I could get on the road too).
AFAIK Sligo RFC would only run a bus if one of their kids teams was doing the half-time minis so probably no luck there.
So only options are probably to hope someone here offers you a lift, or book a room and head back in the morning.

cheers Paul; I'll do that now. Still a good bit of time to go so hopefully a suggestion presents itself!

I'm no good to you I do not live in Sligo.

I would suggest you edit your topic.
To something like

Traveling to Connacht v Ulster from Sligo or something similar.

morning all,

hoping to go to the Connacht - Ulster interpro just before Christmas, will be the first time for me at the Sportsground. Just wondering if anyone might be able to give me a heads up on travel - apologies if this should be in a different forum.

I'll be at my wife's family's home in Sligo from the morning of the 23rd. Is there a supporter's group bus or similar (local RFC?) that runs from Sligo to the games, or a group it would be worth getting in touch with? The initial plan was to get a Bus Eireann up and down, but the last one back to Sligo is circa 8.30, which isn't much use.

Cheers in advance for any help or advice that you can provide.