Sometimes, even great, growing companies cost too much to buy.Costco Wholesale Corporation (COST -1.53%) investors had a good week. From last Friday's close below 744throughFriday,May10,sharesofthewarehouseretailergainedroughly40 in value after reporting strong e-commerce sales in its update for April.And 40couldbejustthebeginning.LoopCapitalanalystLauraChampinepredictsthat,withinayear,Costcoshareswillfetch840 apiece. Is Costco stock a buy? Costco reported Wednesday that ...