A common term for someone who has plenty of money but doesn't like to spend it is "miser". A miser is someone who hoards their wealth and is extremely reluctant to spend it, even when they can easily afford to.
Other informal terms include:
"Cheapskate": Someone who is unwilling to spend money, often perceived as stingy.
"Penny-pincher": Someone who tries to spend as little money as possible.
"Scrooge": This comes from the character Ebenezer Scrooge in Charles Dickens' A Christmas Carol, and it describes someone who is very frugal or stingy with their wealth.
These terms generally carry a negative connotation, implying that the person is excessively frugal or selfish with their money.