Traditional Escrow

I'll buy a house for $ 175,000. I put at $ 150,000. I need $ 25,000. I want to get a HELOC because the costs are much cheaper than a traditional loan. With conventional financing, there is an approval letter stating that the lender is willing to finance the buyer for a specific amount. What is the process of obtaining a HELOC during escrow. Please be specific in the steps and details on how to obtain a HELOC for escrow.

Is a HELOC on your purchase? can not

or

Is a HELOC on your sales? can not

a Heloc is a line of credit secured by property you already own and can not be on the market and even less in excrow.

Use a credit card and get the money later to pay the card.