How much for 18 yr old Arabian?

hello everyone :)

i'm new here...and new in california. i moved here from germany a year ago and wanna buy a horse now. currently i'm riding a lil arabian which is 18 years old. the owners are thinking about selling him to me because they don't really ride him anymore. how much do you think would be a fair price? he doesn't have shoes and i noticed an equine sarcoid on his belly...

i attached a picture of him too :D

any suggestions appreciated :)

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