The preferred accounts are designed to hope you do one of several things:
Pay one day late. Then charge you all the deferred interest. Many people think If they put $X a month aside, then pay just before the 6 months, 12 moths or no-payment before 2014 period ends then I will be able to afford the computer, carpet, or furniture. The interest rate they will charge you if you are late will be buried in the fine print. But expect it to be very high.
Pay on time, but now that you have a card with their logo on it. So now you feel that you should buy the accessories from them. They hope that you become a long time customer. They want to make money on your next computer also.
Their "Bill Me Later" option on that site as essentially the same as the preferred account.
In the end you will have another line of credit. They will do a credit check. The impact, both positive and negative, on your credit picture is discussed in other questions.
Because two of the three options you mentioned in your question (cash, debit card) imply that you have enough cash to buy the computer today, there is no reason to get another credit card to finance the purchase. The delayed payment with the preferred account, will save you about 10 dollars (2000 * 1% interest * 0.5 years).
The choice of store might save you more money, though with Apple there are fewer places to get legitimate discounts.
Here are your options:
- Buy local: Cash or debit. Will have sales tax.
- Buy online: debit or credit or PayPal linked to your bank account. Watch out for sales tax and delivery charges. They must charge sales tax if they have a store in your state.
How to get the limit increased:
You can ask for a temporary increase in the credit limit, or you can ask for a permanent one. Some credit cards can do this online, others require you to talk to them. If they are going to agree to this, it can be done in a few minutes. Some individuals on this site have even been able to send the check to the credit card company before completing the purchase, thus "increasing" their credit limit. YMMV. I have no idea if it works.
A good reason to use the existing credit card, instead of the debit card is if the credit card is a rewards card. The extra money or points can be very nice. Just make sure you pay it back before the bill is due. In fact you can send the money to the credit card company the same day the computer arrives in the mail.
Having the transaction on the credit card can also get you purchase protection, and some cards automatically extend the warranty.