I should have looked up a new computer on the internet today.

Services of Windows 10 will end atin October, so I will have to search for a new one that I can play games withon.

I'd rather buy an expensive one.

I should have looked up a new computer on the internet today.

We need to add the article "a" before "new computer" because "computer" is a countable noun. The indefinite article "a" is necessary to indicate a single item.

Services ofThe support for Windows 10 will end atin October, so I have to search for a new one that I can play games withon.

"Services of Windows 10" is a bit awkward. The more natural phrasing would be "The support for Windows 10." "At October" should be "in October" because we use "in" with months. "Search new one" needs "for" after "search" since we search for things. Also, the article "a" is needed before "new one." "Play games with" should be "play games on," because we typically say "play games on a computer."

I'd rather buy an expensive one.

We need to add "an" before "expensive one" because "one" refers to a singular, countable noun (computer), and we use the indefinite article "an" in this case. Also, "an" is necessary when the following word begins with a vowel sound, like "expensive."

I should have looked upsearched for new computers on the iInternet today.

Services of Windows 10 services will end atin October, so I have to search for a new one that I can play games with.

I'd rather buy an expensive one.

Or you can say "I don't mind buying an expensive one"