I am sort of the opposite of @patliean1 in the sense that I have zero inclination to be an influencer and will probably never make a YouTube video about bikes. However, I do sustain my bike hobby through a bike accessory business which is largely done via 3d prints. It has also allowed me to afford a few adjacent projects/prototypes, including (e.g., a Ti frame, modified track bars for road, and picking parts for a new wheelset to test some thoughts around the Conti 111 tire).
The 1st was a bad business idea, the 2nd was a missed opportunity, and the 3rd I expected the tariff situation to kill, but it's led me to a more long-term purchase mentality for frames. In that vein, three frames are interesting choices, IMO for going the low-cost China route.
- Speeder SC-R55D: I have never bought a frame from them, but I do have experience with their forks and bars / stem combos, and I believe in their quality. The use of UDH is a plus for future compatibility, but also because bent hangers are the thing that i hated most about my open mold frames and why all my bikes currently run the same hanger (the syntace x12)
- Bigrock Sohtea Team (or regular): I think with the Panda Podium sale, this fits in your budget, and with some good FB marketplace / eBay skills, you might be able to also work in a wheel upgrade. The thing I like about this frame is that it uses a round seatpost with an external seat clamp, so getting your position dialed will be easier/cheaper, and this, more than anything else aero will make you fast vs. slow. Also worth noting that slipping or stuck seat posts are a common frustration with cheap frames, so this one avoids that trap too.
- Ican FL1: if you are OK with a little more weight but don't want that horrible brand name, this is an alternative to the Bigrock. I
I haven't ridden any of these bikes, so I defer to others for their expertise, but I would consider these 3 bikes in your price range for those two reasons.