Today, the cheapest non-ex-police/paramedic FJR (and still of VERY questionable condition/mileage, with zero work history) I could get is 4k€. That is a bit under 5000USD, for a 14-15Y old motorcycle that will need at least new tires, full fork rebuild, chain kit, rear shock, filters+engine oil+final gear oil+plugs, valve check/adjustment, cooling fluid, new steering bearings, swingarm greasing and very possibly new timing chain/guide/tensioner, brake pads, brake lines. Not worth it. And if I decide to sell it 2 months later, I'd lose at least 1500€.
Another model I've discovered (here it's still winter- took me 30min today to defrost my car) is the ER6-F (Ninja 650r). An (allegedly) recently serviced one is around 2200-2500€. It is much poorer in top power, but 5k to 9k, where I stay 95% while 2up riding, seems to be ~15% over a stock FZ6 (more likely 5-8% over mine, with the Leo Vince exhaust), fuel range is similar. I did ride an ER6n rental in the past for a couple hours and wasn't too impressed, but it was lowered and had horrible no-name rubber. The suspension is crap (not even front preload adj), but for ~400€ I could get a new bitubo cartridge kit (only preload adj, but they factory set it considering your weight and riding type). Have found one locally for a good price, and will try to get a test ride as soon as the snow clears (that should be next week). Main thing it'd lack though is those 2nd gear 10000rpm WOT overtaking I sometimes do with the fz6 (which I'd "demote" to mainly solo riding), but should I decide to buy one and not like it, it wouldn't a big loss to resell it.