Do you pay your bid for the first or highest bid on Ebay?

You only pay what you actually offer. If you entered a maximum bid higher than the offer never got up to, you just pay what the bidding got up to. So if no one bids against you, you end up paying only the initial price.

For example 
 
If you had the first offer of $ 10, but then realized he would be willing to pay up to $ 30 so changing your maximum bid of $ 30, but nobody comes and bids against the final price would be $ 10.