We were out in Fuerteventura at Easter and
all fragrances were a lot more expensive than at home

I was really surprised, because we've always had bargains in the Canaries before. It's not just the low exchange rate which has made it more expensive, they seem to have put the prices up anyway.
My son wanted me to pick up some Paco Rabanne 1 Million for him and honestly, the cheapest I saw it was at Manchester Airport on the way out. I was wandering around the perfume shops one day and discovered the new J-Lo Sunkissed fragrance, the cheapest I found it was 38€ 100ml, so I texted my son back home to find out how much at Boots and it's only £27!!!
If you're after something that's been around a while you'll get it cheaper online than anywhere else:
Fragrance Direct and
Cheap Smells are good sites to start looking, or just Google for what you want. If you're after something that's fairly new you'll probably get it cheaper at the airport