How much is this worth?

The fact that the visor is multi-signed by what appears to be whichever driver walked by could actually decrease its value. Also, since you didn't say who used the visor, it's hard to put a value on it. Most IRL race used visors, signed by the driver who used them, sell for between $50 and $200, depending on who the driver is. Big name living retired drivers can fetch up to $1000 for an signed, race used visor.