The MK 7's were all Isreali (sp?) pistols. The reason you care about getting a Mark 7 pistols is that the trigger was improved (better action/pull). The Mark 7 50 A&E is interchangeable with current Mark 9's make in the USA by SACO in New York. The other Mark 7's are unique (you can't easily change a 44 to 357).
With the Mark 9's, the parts became more interchangeable, manufacture moved to the USA (SACO in New York), and all the previous refinements were retained.
New Mark 9's should carry about a $200 premium over Mark 7's in the same shape (NIB, slightly used, etc.). For my money, I think a Mark 7 is better deal, especially if you do not plan to convert from 357 to 44/50A&E.
As for price, well, it really depends on your local market. I don't think you got a screaming good deal but, you didn't get taken either. Again, valuation really depends on condition and where you live.
When I open my safe and reach for a gun I love to shoot, the D.E. MK 7 44Magnum is hard to resist
Enjoy it! You have a great pistol,
Sid
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Tx FFL