Used Linn sondek lp12 worth?

Hi guys,

It's been a lont time since I've last posted....and I would seriously need your help.

Well, for the first time of my life, I have decided to get into vinyls (and therefore consider myself a newbie) and might have an opportunity to get my hands on a used TT.

I could get a Linn sondek lp12 circa 1988 from one of my best friend's mother. It has the Valhalla power supply, a SME Series III tonearm and an AKG P8ES Supernova VDH II S  moving magnet cartridge.

The lp12 has received both a Trampoline 2 and cirkus upgrades in 2015 from a Linn dealer. Also the cartridge has been rebuilt with a new suspension and a new VDH shibata stylus, again in late 2015.

Overall condition is very very good.

My friend's mother is nearing 80 years-old and is struggling with serious health issues. She has therefore decided to part with (among other things) her lp12. No shipping would be needed as she lives 30 minutes from my place. I could pick her TT up personally. 

She wants 900$ for it. 

Now, I have absolutely NO IDEA what her TT is worth?

I have tried to search the Web on various audio sites to get an idea about the lp12's prices BUT they really are all over the place !!!

Should I go for it at 900$ and take the plunge ? Am I getting ripped off or is it the other way around (I wouldn't want to take advantage of her either)?

I want both her and me to settle for a fair price. What would be a reasonable $$ settlement? 

Hoping for your advices

Thank you very much for your help.

Sincere regards