Is it permissible to take a loan from a bank to complete the purchase price of a house, given the existence of a large penalty clause in case of withdrawal from the purchase, and the inability to obtain the amount from another source?

Borrowing with interest (riba) is forbidden except in cases of dire necessity. Look for Sharia-compliant alternatives, such as financing through Islamic banks. Fear Allah, and He will make a way out for you and provide for you from sources you could never imagine, and He will make your affairs easy for you.

You can also seek help through some well-known supplications for debt relief, such as: "O Allah, suffice me with what is lawful against what is unlawful, and enrich me with Your bounty, by Your grace, against all others," and "O Allah, I seek refuge in You from anxiety and sorrow, and I seek refuge in You from inability and laziness, and I seek refuge in You from cowardice and stinginess, and I seek refuge in You from the burden of debt and the oppression of men."