Sainsbury's: Taste the Difference ones are 3 syns each (142g), or the frozen or chilled meatfree quarter pounders are only 0.5 syns each (113g).
Tesco: Finest chilled beefburgers with sun-dried tomatoes or shallots or chives, 3.5 syns each (114g), Finest chilled beefburgers 2.5 syns each (85g).
Asda: Pork and apple burgers, chilled, 114g - FREE! Vegetarian burgers, frozen, 0.5 syn (57g).
M&S: Organic beefburgers, chilled, 2 syns (57g), venison & sweet red onion burgers, chilled, 1 syn (142g).
Hope those suggestions help for people planning barbeques!