This is an area where banks can help. A bank can loan you the money immediately after the job is done with a low-ish interest rate (since your client is publicly traded and reputable and presumably highly creditworthy) and then ask for repayment only when the 45 days EOM is up. Alternatively you just ask the bank for a fraction of the invoice amount upfront and not think about paying interest to the bank any more. It's called invoice factoring.