Likelihood is it's a Benotto 800, maybe a Benotto 1000. 1200 or 1500. With the pics shown, who knows. Non-original fork, and it would be nice to see a pic of under the bottom bracket shell just to confirm it has expected cut-outs and stuff. The non-original fork, why is it there? Front-ender bent the original? I'd carefully check the top tube, the downtube and their respective lugs at the head tube to confirm there's no signs of collision damage.
Just to give you perspective, a top-of-the-line Benotto 3000 fully refurbished sold here on BF - where the bike enthusiasts hang out - for just $380, but it was complete and ready to ride.
1981 Benotto 3000, 54x54
And I sold a highly sought-after Benotto 3000 frame and fork with the nice De Rosa-esque diamond chainstays for $100 over here:
80s Benotto 3000 frame & fork (54-55cm)
Honestly, I think your offer was more than fair for what I'm seeing there. That's way overpriced for a Benotto-1500-or-lesser model. I'd point the seller to this thread. I understand them tossing back an offer of $150, your $100 offer must've felt like a massive lowball, but it's actually a
high market-fair price at $100 assuming the seat post isn't stuck and there's no signs of frame damage from a wreck. The fact it doesn't have the original fork, I'd be hard-pressed to pay more than $80 for it.
The seller needs to understand it's gonna take at least $300 in parts to rebuild this thing, and there's no way in hell it's selling for $450 ($150 + $300 in parts) once you rebuild it. $80-100 is a fair-fair price for everyone, with me leaning towards $80 due to non-original (and quite ugly) fork. $120-150 is a steal for the seller. $50-60 would be a steal to you.