First post on this site so will try not to sound too stupid!

Have had a '66 1098cc minor for a couple of years now. While living in the north of England, it was perfect as only had to drive 15 miles to and from work. A year ago I moved back to Wales and with a new job, the commute of 110 miles a day was obviously killing the poor thing - am amazed it managed so well for the short time I used it for such long distances.
Anyway - had to cover it and put it in the garage. What with work etc, I never got round to fixing it up, cleaning rust etc so just got left there.
Managed to remember to turn it over or take it for a spin once in a while, but that’s about it. It’s been about 6 months since it was last looked at as have been away with work a lot.
Now it seems the gearbox may have seized!
I topped up the oil, used leads to jump it to start, and left it running for a bit. When I then tried to put it in gear with engine on - it wasn’t having any of it.
Nice, pleasant screeching sound - in all gears.
I'm not, in any shape or form, a mechanic - but hoped I would learn some basics with this car - unfortunately lack of time etc
Does this mean the gearbox has indeed seized, and if so, what is the easiest/cheapest solution?
Now have to sell it as it is just sat there with nobody able to look after it, and I hate to see it just rust to death so am looking for the easiest/cheapest option which doesn’t require a new gearbox, letting it slowly die or scrapping it.
Can anyone help as I have an affinity for the thing which makes me want to do alright by the old thing.
Thanks in advance for anyone who takes the time to educate me.