The Wanted Zin from Morrisons.
It’s normally £10 but is often on sale for £7 which is when I stock up. It’s Italian wine (so Primitivo technically rather than zinfandel,) but aged in American oak. Primitivo/zinfindel just different names for the same thing same as Shiraz/Syrah.
Any Californian Lodi old vine Zinfandel is going to be pretty good but your then talking north of £14.
Campo viejo reserva rioja (the 1 with the orange label,) is very good indeed and if you spot it on offer around £8 it’s a must buy.