With EA confirming the return of SBC’s and the return of the OTW Gurantee there is a good chance their will be the return of some form of UCL SBC requiring CL cards.
In the past when these cards are required, due to low supply and high demand, we seen all rares go extinct. At the moment you can pick up UCL rare cards from decent leagues/nations and ratings for under 4k.
A few examples; Lozano, Fernando, Soares, Tadic etc. https://www.futbin.com/stc/cheapest?version=ucl_rare more on this link.
Only go into this investment if you are willing to lose some coins as the demand for this potential sbc may be low and/or they may release a guaranteed UCL rare sbc with it. However if successful you could be looking at over 100% profit margins.