Get a bank loan
One option to cover your start-up costs is to get a bank loan. Before approaching you bank, you'll want to have your business plan prepared.
The advantages: unlike overdrafts you're guaranteed the money for the term you agree and the loans can be tied to the lifetime of equipment or assets that you are purchasing with the loan. Most importantly you won't have to give the lender a percentage of your profits or a share in your company
Disadvantages: you may struggle to meet monthly payments if your customers don't pay you or if you have to pay for unexpected items and if your loan is secured against your personal property or assets then you could lose them if you don't keep up the payments.