Carbon Dioxide

[jon]

I have just decided to re plant my tank after 4 years plant free, i took my carbon dioxide bottle to the garden centre i always used for a refill, but was shocked to find the cost had risen from about £10 for a refill to about £25, i reluctantly paid this price but do not wish to go back when the bottle is empty i live in south wales and was wondering if anyone could advise me of any alternative stockists reasonably close by i can use ? I have a "dupla" 0.50kg bottle. Any assistance would be appreciated. Thanks