ah siao, soccer is not really that fast. unless you buy old LCDs with poor response time, the current crop should be fine. But then again, to set expectation, the current TV resolution sucks so don't expect your LCD TV to look that great.
Yes, big store will charge more. The key thing is to shop around and compare. But please take note, you pay for what you get. You can only make meaningful comparison when comparing same model, same manufacturer across the stores. If you are not in a hurry I suggest to wait for the next PC/digital show - there will be a lot of LCD/plasma TVs - mostly they give you good price and you can even bargain - especially the last day.