I think it's more economical to rent these cards, especially the L1 GF legendary cards.

E.g., L1 GF Djinn Biljka is ~$27, the average rental price is 6.5 DEC, for this money, you can rent this card for more than 14 (!) years:

Let's assume $0.8/1000 DEC

Card cost: $27/$0.8*1000 = 33750 DEC
For this amount, you can rent 33750/6.5 = ~5192 days (more than 14 years)

And you are safe from card price inflation as well 😉

When I had a land, I rented 5x L1 GF CL cards, and sometimes the overall cost was ~10 DEC/day (for 12500 PP).

And also, you can find max-level epic cards for only 1 DEC/day