My suggestion is that you want to buy parts, NOT an entire rifle.
For a flashider AND a bayo lug, you're gonna need a preban lower. Preban complete lowers are in the $800-1,000 price range. Postban complete lowers are in the $300 price range.
Now, they do make a birdcage-looking "muzzle brake" that is postban legal. You may wanna look into that, which will get you the look you want on a postban lower. (NOTE: You CANNOT have a bayo lug with this configuration - too many "evil features." )
Here's an opinion - get the birdcage muzzle brake and the postban lower, and forget the bayo lug. Is a bayo lug worth an additional $5-700 to you?? Not that you need to justify the expense to me, or anyone else. Gun ownership IS and SHOULD BE all about what YOU want.
The flashider is essentially for night time use - to minimize blinding flash. How often do you find yourself shooting at night?? Comparatively, the muzzle brake will benefit you EVERY TIME you pull the trigger - minimizing muzzle jump, and letting you re-acquire your target faster.
I'm not aware of any current manufacturers / assemblers that sell an upper with triangular handguards. Occasionally you will see them at gun shows (used).
Personally, I'd buy a new upper, and then retrofit it to the tri handguards. (Buy the handguards at a gun show, or a parts dealer. NOTHING more frustrating than assembling a "new to you" gun with a shot-out barrel that patterns like a shotgun.
HTH, have fun.
[Edited to add...]
I should add this - I DO own a preban lower, but for the option of having a telescoping stock, not a bayo lug, or a flashider. I presently have a postban upper on my preban lower. A postban upper with a muzzle brake. (Just to show that my money is where my mouth is at
)