I'll reinforce what others have said. Mainly, be patient. The cards will be there next week and next year*.
1. Set yourself a budget and live within it. Buy $50 worth of credits when you can afford it. If you are patient, you will be able to take advantage of recharge bonus that will get you 600 credits for $50. These bonuses come by 4-5 times each year.
2. Enjoy the previews and use the wishlist to mark cards you plan to buy.
3. The best deal around is the 4th card refund offer. You buy 4 cards and get a refund for the 4th. That's at least a 25% saving. However, if you buy 3 lower quality cards and then a 3K card you percent saving will be greater. The deal comes around 4-5 times a year.
4. Never buy cards at full price. If you are patient you can get them cheeper via a special offer.
5. Don't buy cards you won't play. Play a 720p card or demo on your computer and compare its quality to a 1080p and to a 3K. I've found that 1080p and 3K are acceptable on my computer. However, some of my favorite models are only available in 720p. For them, I occasionally reset my scale and play only 720p cards for a few days. The same is true of the "classic" 480p cards, but more so. Buying a low resolution card you won't play just to get to the next higher discount level is not a good deal.
The best overall strategy is:
1. Wishlist the cards you plan to buy from previews or based cards you already own.
2 When a recharge bonus comes along buy as many credits as you can afford. If you can't afford at least $50, wait till the next recharge bonus.
3 Don't spend anything until the 4th card refund offer comes along. When it does, spend all your credits on sets of 4 cards. For each set, buy the 3 cheepest cards from your wishlist and then for the 4th buy the most expensive. Repeat until you are out of credit, but plan ahead to ensure you have enough credits to buy a set of 4 cards.
4. Now wait for the next recharge bonus and repeat.
Some of the TGIF specials are good deals for buying cards at a low price, but most don't give you a choice of which cards you get. With a small collection the chance of discovering a gem you wouldn't otherwise buy is worth the risk of getting a card you don't want if the price is right. With a large collection the possible reward is less because you probably already own the cards you like.
- Some cards do not stay in the store forever. In, I think, 6 cases in the past 10 years a model has demanded that her cards be removed. The first time this happened Totem when to court and lost. Now they simply comply with the request. Sometimes Totem will give advanced notice if this is about to happen. Sometimes they can't. So there is a small chance that a card you plan to buy will disappear. This is a very small risk. If you already own such a card, you can keep it and continue to play it.