Living as I do in southern Thailand, the only stamps I can buy locally are new issues from the local post office. There is not a single stamp shop on the island where I live. While there are still a few stamp shops remaining in Bangkok, along with at least one large show each year, neither my schedule or budget offer many opportunities for travel to the capital. Thus, the vast majority of my my collection is built up through online purchases, primarily via eBay auctions.
This means that I am constantly having to take into consideration the shipping costs of whatever stamps I want to bid on. This is also the reason that I rarely purchase much-needed supplies such as catalogues or album binders and even things like mounts and stock books fall by the wayside. While my inventory records only the base purchase price for each stamp, my philatelic-purchasing budget needs to factor in costs with shipping included.