Wow, great thread! And I have little to add. I wouldn't spend more than $20-30 AT MOST on a scope for that rifle. I LOVED my Powerline 880 and Pumpmaster 760 pumps. But after I left the military (Infantry) becoming expert on several weapons (from M16A1 to anti-tank (dragon) missiles) that when I got back out of the military, I realized how bad my old pumps were for anything more than plinking. The accuracy just wasn't there... and I was getting interested in hunting squirrel so I wanted something that could guarantee me a kill without the animal suffering or needing multiple shots.
I ended up not shooting for many years. In the beginning of Covid I decided to go with a 'relatively' low priced break barrel with good reviews. I think it ran about $300. It's a pellet repeater with a 'magazine' of 10 .22 pellets. I do wish I would have done just a little more research though, as this rifle has NO iron sites do to the positioning of the magazine. This was corrected in the VERY NEXT version of the rifle.
The scope that accompanied it was pretty bad though. After a few shooting sessions the thing got bumped just a little when my daughter was laying it down and that was it.... scope was suddenly WAY off and I could never get it zeroed again.
This scope quality was mentioned in reviews of the rifle, but the rifle itself was so highly rated that I didn't chafe too much knowing that the scope was junk and likely didn't add a ton to the original price.
I'd be willing to spend maybe ~$150-$200 at MOST. I don't want to buy a scope that costs anything beyond 1/2 to 2/3 the cost of the rifle.
Here are a couple places that I've made purchases from, and which might carry a suitable scope for you. They may sell the 880 and may even carry some scopes they recommend for the Powerline 880. Wouldn't surprise me at all!
Sorry for the long wind... it is my wont.
Pyramyd Air Rifles
Airgun Depot
And though I'm personally not an NRA member, they do have an entire program for air rifles:
NRA Air Rifle Program
~Netopia