Need help finding of a piece of commercial property

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I'm looking to purchase the property that my family has ran our business out of for 30 years.

how do I value the property?

Is it valued by the income it produces?
the tenant lease it yields?
the future value/potential of the property?

a combination of all of the above?

the property is a convenience store / shell station.

the land is about 1/2 acre with about 100ft of frontage on a very busy highway.

we currently pay $4,300 a month for the lease, which we can easily afford and still pull a very good income.

any advice would be great, and more information is available upon request.