Thats not an FX1, I believe that's a Forza. The Forza is a tube framed seat. Tube framed seats are not illegal in Lemons. However, the head of tech is not a fan of them and sometimes requires additional seatback support to be added. I'm personally not a fan of them as my old FIA tube framed Sparco used to leave me bruised after a weekend. Easy way to spot a tube framed seat is if the back of the seat is covered in fabric.
But you are on the right track here. I've bought several used quality composite seats in the $100 range and sometimes less. Especially this time of year in the racing off-season. A ripped seat cover in sideways hat Sammy's Honda can lead to a bargain for you. As far as aluminum seats go, they are often the cheapest but most seem to be drag race or circle track based seats. The drag race ones usually have no upper body side support in the shoulder area. The circle track ones may mostly have support on the right side. That said, it doesn't stop me from searching on Kirkey for an Intermediate Road Race or Style 47 seat. Ultrashield and Butlerbuilt also make road race seats but like Kirkey the vast majority of the used ones are drag or circle track.
That Corbeau Forza retails for $250 so it better be awful cheap and fit me well for me to consider it. IMHO, hands down the best value for a new composite seat is the BiMarco Hummer which is $300 delivered and it is a containment seat.
1990 RX7 "Mazdarita" 1964 Sunbeam Imp (IOE 2013 Sears Pointless) 2002 Jaguar x-type (Winner C-Class 2021 Sears Pointless)
Gone bye-bye
1994 Jaguar XJ12 (Winner C-Class 2013 Sears Pointless) 1980 Rover SD1 (I Got Screwed 2014 Return of Lemonites)