The kits are mostly cheap hodgepodge shit for the people who want to build $400 AR15’s. I’m not aware of mid to high end kits like your budget is allowing.
If you’ve already got the lower I’d be looking for a complete upper around a grand and then $500 to complete the lower. If you wait for a sale you can build a hell of a nice lower for $500. I’d get a Seekins parts kit for just under $100, Geissele SSA-E or SD-E trigger depending on whether you prefer a curved or straight shoe for sub $200 on sale, and that leave you $200 for buffer assembly and stock. For that budget I’d get an LMT enhanced tube, Geissele super 42 buffer and spring, and a Magpul ACS.
There’s a lot of great uppers for a grand. I’d be buying one of the new 224 Valkyrie uppers from Seekins that were just released.