If you're not looking for one holo card in particular, your best bet might be to check the Ebay auctions for a bundle of them that you like. This can work out a lot cheaper than buying cards individually, especially if you avoid having to pay postage for each individual card. Only buy bundles where you can clearly see every card you're going to be getting though. Avoid the ones where sellers say they're going to send you X amount of random cards including 1 random holo.
Also avoid buying individual booster packs. There's no guarantee that you'll even find a holo, and these odds are made even worse by how easy it is for sellers to weigh booster packs to tell if there's a holo inside. There are people out there who buy booster boxes, open all the ones that weigh the heaviest, then sell the rest.