Have to echo seau grateau here, not sure what you're looking at but my out-the-door for the Big Block frameset at Sacramento LBS was $592.63 in August 2020.

Thunderdome looks like a great bike and what I put together w the BB frameset ended up 2x Thunderdome's complete but I chose the BB specifically for the clearance to run 32 tires.

Was it worth it? 100%. I'm sure same would be true if I'd gone with Surly, Salsa, or any of the other well regarded marquis but this is the finest, most solid and responsive experience I have ever had on a fixie bike (that's an italicized i character btw ^^).