Can you def not get to a specialist that stocks kimbolton? For that budget, I'd get a gold box. Even more so if you've got a few small ones already; because you'll get a bit more variety (& 10x the quality). Some of the bigger boxes are similar items to the small, just loads of them.
Otherwise the BS party box is good. But could be very repetitive alongside other boxes. From the range.
Orr, if it were me looking at supermarkets, I'd buy a few of the 3 for 20 cakes (or a combo if you want small rockets) and a visage box from lidl and spend the change on some shot tubes from asda or similar