Honestly - replace it with another used one - or another gun alltogether. All the options mentioned will WORK just fine but are not particularly cost effective. I'd only bother with reboring or sleeving if I wanted something REALLY odd that wasn't available factory. The thing is guns used to be far more expensive than they are now and gunsmithing used to be a lot cheaper. These days outside of things that you just can't buy factory (eg, something like a 7-30 Waters lever gun or other custom chamberings) its usually not worth the smith's time (or rather, the money you'll PAY for his time) to futz with such things.
EG I just rebarreled a Savage Axis - but ONLY because I wanted a 6.5x55 barrel and that's not available from the factory (and it's mostly niche factory options that still offer that). The replacement barrel cost more than the original gun did.