Ways of referring the notion "in a rich way" to colloquial English

Solution 1:

You are going on a spending spree :

a brief period of extravagant spending

Louis went on a spending spree, buying new clothes for all of them.

(Collins Dictionary)

Solution 2:

In addition to indulging yourself, living large, and possibly going on a (spending) spree, you're also living high on the hog or eating high off the hog:

I have to do my shopping in the black market because we can't eat as high off the hog as Roosevelt and Ickes and Joe Davis and all those millionaire friends of the common man.

This idiom is often used negatively, describing the spending habits of others, but in older U.S. literature it's also used to describe one's own behavior. For example,

Of course women always have loved me for my money and as soon as Trixie finds my pot of gold, we are going to be living high on the hog, let me tell you.

I ended up not needing a new car, so I spent my savings living high on the hog for a week.

Solution 3:

I like the idiom live large:

[Merriam-Webster]
US slang
: to live like a very wealthy and successful person
// a star who is living large

In your example, you could say:

I have very little money, but I decided to live large for a week anyway.

This implies not only that you you spent a lot of money, but that you spent it in a lavish manner as the rich would do.

Solution 4:

Solution 5:

You could refer to extravagant spending by saying that you pissed money up the wall or that you pissed money away. For instance, an article on the goofy site Daily Mash has the title "Man who got surround sound looking for new ways to piss money up the wall." The first two paragraphs are rife with expressions in the same sense:

A MAN who bought an expensive Bose surround sound system for his tiny living room is looking for new ways to spunk away his income.

Sales executive Nathan Muir feels he should fritter more cash after the top-of-the-range ‘kit’ failed to make any noticeable difference to his quality of life.

The usage is especially appropriate for extravagant spending on restaurants or drinks. Based on sources like the above, the longer expression is more common in the UK. In Merriam-Webster, piss away means

slang, sometimes vulgar

: to fritter away : squander

and in the Free Dictionary piss money up the wall means

To waste a lot of money; to spend money frivolously.

The Oxford English Dictionary includes both usages under "piss, v".