Hi you should try Wally's in the Royal Arcade in Cardiff.
I use the hot powder as part of my base sauce recipe. and it works out about 20p per batch of my base recipe.
Basic curry sauce   
vegetable oil
4 medium onions 3 fine diced 1 sliced
1/2 tsp ground peppercorns
1 tsp salt
fry until translucent then add
20g minced ginger
20g minced garlic
15g Bolsts hot curry powder
fry for about 5 min avoid burning then add
250 ml water simmer for a while then add
500g passata
2 heaped tsp dried methi leaves
simmer for 30 min