I need some SAGE advice!!

[enameldoc]

I'm not going to lie. I'm a newby.

I am considering buying a 1981 Oyser Perpetual Day-Date (1803)
It is all original with 18ct solid gold everything (President bracelet, case and bezel) and is in near mint condition. No box or cert. but from a reputable dealer (in Singapore).
Actually it is on eBay and the item no. is 310008978114.

I have gotten advice from all different sources but I would like you people to kick in your two cents worth. What is a fair value for something like this? Is it all over the map?

Thanks for your valuable time.