Hello.
I recommend you to post the full screenshot of your pokemon, that includes stats, ability and nature, as the price of pokemons depend on those three. You will most likely get an accurate response with that. :)
As soon as you have enough post counts (I believe you do now), you would be able to send/reply to PMs. :Grin:
Welcome to PRO, I hope you enjoy your stay!
You might get a little more help on this thread if you post it on the Yellow Server Price Checker forum. This forum is more dedicated to selling of pokemon more than price checking.
This.
Moved to the appropriate sub forum anyway.
Go north. Once you get through the bridge, go east and enter the house, you should be able to talk to Bill.
Afterwards, you're going to be told to help find his book (which is under his pillow on the bed).
Yes, you can catch Gothita in route 37.
The price of the Pokemon depends on the IVs/Nature/Ability of the Gothita.
Gothita is a really rare Pokemon to find, and from what I have seen, there seems to be a huge demand for Shadow tag bold Gothita.