Math - current cost - cash received if sold

[emptycucumber]

Properties increase by 10% of the original price with each new purchase.

Current Price:

F37*(1+E37/10)

Properties are built on a required property. If the required property has not been purchased, the Current Price is:

IF(metropolis<2,VLOOKUP(metropolis,shipping_metropolis,2,FALSE)+F37*(1+E37/10),F37*(1+E37/10))

If I sell this property, the Cash Received:

E37*(G37+F37*0.9)/4

However, it's incorrect if the required property is "not owned" in the spreadsheet. I need help figuring out the formula to exclude the price of the required property (the VLOOKUP) for the Cash Received.