If it really is a reasonable price, buy it.
I had a martini 22lr that I sent to a gunsmith (who shall remain nameless) for a re-chamber to 22mag. Should have been a fairly simple operation and it is perfectly safe. He was way late on the job and then told me that when he was working on the crown the liner came loose. I did't know the gun had a liner but took his word for it. MANY more dollars later I had my gun returned to me with a Shilen barrel chambered in 22mag. A scope base hole was stripped and the forearm hole was mislocated, but that gun shoots!
I have too much money in mine, and it's buggered, but if you can get one reasonable I'd say you'd have a keeper (assuming that the bore is good).
Lefty
BTW, If you find a good Martini 'smith, let me know. I sent a full size martini to another gunsmith along with a new replacement barrel and payment in full over a year ago and though he sent my gun back to me (he didn't do any work on it, he fell ill), I'm still waiting on my refund and barrel to come back.