Hi jalal,
As Sara says, there are quite a few shops on the right as you first enter Corfu Town - and as you say, some are very expensive. But there is one called Epiplomania (spelling may not be quite right) which is quite cheap, plus they will deliver large items free of charge. It's not a very large store from the outside so it's easy to miss, it's 2nd. shop after a junction (I think the first shop is kitchens?) and there is a petrol station opposite(ish) - If you get to Profi then you have gone too far.
Sorry it's a bit vague - never was any good at directions!