Several T3's have been sold at Arizona Customs over the last 6 years. How much they sold for depends on the variant, condition, and of course, how much someone was willing to pay.
Here are the selling prices of some (again, these are selling prices, not asking prices)-
In 2020 two were sold, one for $395, and the other for $780.
In 2019 one sold for $1500. (that's not a typo- fifteen hundred dollars)
In 2017 two were sold, one for $595, the other for $600.
I remember I bought one new, around 2005, with micarta handles, for $300.
To get a starting point, I would suggest doing some research at AC's to see which variant you have and what it sold for.