Well now....
... eBay has this listed for only $4300 + $50 shipping IF you can get it at the opening bid. That is ... used.
... And if the $4300 is a bit out of budget for a father's day gift ... then consider that in the last 30 days they sold this little 600mm Sigma CAT gem for only $329. Speed of the lense was not indicated.
Or there is this little active listing (7622687942) for a 400mm f5.6 APO Sigma with an asking price of just $799.
These two seem a little more "affordable" then the $4300 lens. Of course, I would be happy to get a nice tie and shirt - which is about as predictable as it gets. LOL!
And while we're on the subject of what YOU want for fathers' day - here's a couple for me....
Unfortunately - the only listing I could find was an obviously fraudulant listing using a stolen eBay ID - it is for a 600mm Image Stabilized Canon prime lense - asking only $1 clam with no reserve, a $1000 "buy it now" to bait suckers and 17 hours to go on the 1 day listing

! LOL! If only it were true then pigs would have wings and fly, eh? Here's a photo though of the little $6000 gem... (if the image does not display it is because EBAY took the listing down I imagine.
I did report the listing to EBAY security as suspected of being made with a stolen eBay account.
And as for a potential Father's day gift with more potential from a budgetary POV - how about this little $15 "gift" for the good ol' Dad??? ....
And no... the bunny outfit is NOT for me!

Of course, I am about as unlikely to get my spouse into a bunny outfit like this as I am to get the 600mm IS Canon prime at ANY price.