There's a Ruger Mk1 22cal handgun for sale locally for $250...
I bought one of the 6 7/8" Target models new, in 83. For about half the price of the one you are looking at. It has been an outstanding .22 semi, so I never had a need to buy any of the later Marks.
Lack of a last shot hold open was a bit of a disappointment, but not a deal breaker. Mine has run well, nearly flawless, but not 100% (never found any .22LR semi pistol that was), runs better than most. One mag jams, once in a while...
Trigger is good, gun is accurate, feels good in my hand, its a joy.
Until you try to take it apart. My advice is ..DON'T. I don't care if an Internet Expert U Tube says "its easy..watch this.." if you don't HAVE to do it, don't. Re-assembly is a little tricksy, if you know the "trick" its not terribly difficult. If you don't, it is IMPOSSIBLE to correctly reassemble the gun.
It's a .22 Sport and Target pistol, not a GI service automatic. It was not designed with the idea it would be constantly stripped and reassembled. If you want to do that, or feel you have to do it constantly, get a different pistol. Get one made for that.
Everything you need to clean to keep the gun running well can be reached and cleaned WITHOUT stripping down the gun.
IF possible get the one with adjustable sights. You may never need to adjust them, but if you do, they're great to have. I've never been a fan of fixed sights on a .22.
Another word of caution, get a GOOD holster. And by "good" I don't mean a specific brand or style, I mean one that will not snag on, or be "eaten up" by the sharp front sight.
I think the Mark I is an excellent value, if not the best value for the money you'll find. There are nicer guns, there are prettier guns, but damn few BETTER guns, and none I know for the same kind of money.