For that much money I would by a Tiapan Veteran standard and a compact and have $300 bucks left over. If there's any left at that price. Thats what I did anyway. A solid build and still fairly light. You seldom hear anything bad about them , Easy hammer spring adjustment. Or check out the new ones with the side lever.
Has he seen or shot a bullpup? All the befits of a long barrel in a short package. No loud ping , and very quiet from the factory. No need to spend more on a moderator with the Taipans.
The Airgun Technology Uragan and Vulcan 3 are very accurate and reliable.
They have CZ barrels and high shot count.
I have owned most of the guns you described. The AGT guns are my favorite all around guns and they appear to come tuned for JSB slugs yet shoot slugs extremely well.