If the intent is to play with RISC-V cheaply rather than getting the absolute cheapest computer, I'd look at something with C908 (a small cpu that is vector capable, RVV 1.0).

A particularly good deal is the Banana Pi BPI-RV2: It has 4xC908@1.25GHz, 512MB DDR3, M.2, miniPCIe, 1x 2.5GbE, 5xGbE.

There is a cheaper Banana Pi BPI-CanMV-K230D-Zero. 2xC908, 128MB LPDDR4, KPU, MIPI CSI/DSI, Wi-Fi, 40x GPIO.

If serious about RISC-V, then of course RVA23 is desirable. Unfortunately any SBC with that is currently expensive due to the RAM shortage situation.