On the bottom bracket will be some letters and numerals, they will show the size by Masi Measure and the serial number which will advise the build date, '84 is right in there. Sante is not.
Size will have some factor as to the value, all I can tell is that is is not really small. Black is a plus.
Be careful with the term Mint, mint is to me and many others is near perfect.
Having the original Masi water bottle is a plus.
The type of wheels is has will also play a part.
"San Marcos" mass are gaining a following but have been undervalued in the past.
They were built in small batches and by some good builders. Joe Starck built a number in the middle 80's.
The negative is that is has Henry James sourced lugs, to many just not the classic design of the "ref. 32" design used by Masi for a over a decade prior.