Why does a buyer value a dollar in a small purchase (e.g. TV) differently to a dollar in a large purchase (e.g. car)? I am referring to how buyers will haggle over 200 when purchasing an item worth, say, 500 but not bat an eyelid paying an extra 5000 on, say, a house.

I am seeking a very brief explanation of this phenomenon or the official name (if it has one).
One explanation from psychology and behavioral economics is "mental accounting": people put different transactions into different mental accounts.

When buying a house, people are imaging (probably unconsciously) a bank account dedicated to that purpose. The account's balance is pretty large (including mortgage loans). \$5000 in or out of this account does not really have any significant impact on the account.

When buying a cellphone, people are imaging a separate bank account, of which the size is much smaller than the home purchasing account. \$500 in or out of this mental account makes a big difference.

If we pool all accounts together, then \$500 saved from buying a cellphone should be the same as the \$500 saved from buying a house.