I don't know about BA, but I noticed on Air Canada's website that they have put out a table re how many miles you can buy (up to 15,000 miles) and how much it will cost you - it's reasonable. Perhaps BA offers the same sort of deal.

Out of Canada there are some really good seat sales on right now. In fact, some are good enough to make you think twice about using your points!

Regarding a credit card affiliated with an airline - I think it is well worth the annual fee. Apart from the usual stuff, I put all my groceries, monthly train pass, etc. on my credit card. Those mileage points add up pretty quickly.

Marty