So was able to score a Fuji Cross a bit ago and I've been riding it around and think that the geometry of a gravel/road bike just isn't for me. I'm more comfortable on a mountain bike, dirt jumper and a "hybrid" road bike (for the work commute and general riding around). I was thinking of selling it (it's a bit big for me at 54cm, I should be on a 50cm-52cm road) and starting over.
I would like to get a new frameset to start a build on. I prefer to build my own because every built bike I got I changed out most of the components any way. It's like computers for me, I build my own so I can get what I specifically want/need.
This leads me to start looking at frames on eBay obviously because again, money is an issue with me. Spending $1500 on just a frame is crazy to me. $500, not so much especially if I can get full carbon and a fork too. So used or anything cheap but good is for me. I keep seeing those cheap full carbon frames from China on there. Does anyone use those for urban commuters? I don't know that I would trust them as a dirt jumper or mountain bike or anything competitive. But wouldn't they be fine for daily riding without so much strain (other than lots of miles)?
I love late 80's early 90's fully rigid mountain bikes for commuting. Bombproof, take fenders, take rear rack, not a big theif magnet, some ride really sweet and can be converted to drop bar for gravel or touring. If you want a newer 700c frame I'd look for something steel from Surly or Soma and build it up. If you can get a Salsa Vaya used I'd consider that too.
I would be extremely leery of buying from some mystery factory online. I've heard some horror stories. If you really want a cheap carbon frame with a bit more assurance check out DIYcarbonbikes here on PB. I've bought two sets of carbon wheels from him and they're great. At least with him you have someone in the country to talk to if you have issues.
I bought a Chinese carbon frame from a company called Trifox, it seems great value and I'm over the moon. Delivery took too long but it finally arrived, I also bought some components from Chinese companies and very happy with quality and price so far. I say give it a go as I've saved $$$ . I also bought from local companies to support them too. Good luck with your endeavor!