I think you are looking at this all wrong...

Let me pose a question to you: Do you own a set of channel lock pliers?

Assuming the answer is yes; How often do you use them?

Assuming the answer is less than once a month; How do you justify owning something that you use this infrequently?

The answer of course is that pliers are a tool and although you may not use them every day; they eventually earn their keep (in this case by allowing you to tighten a leaky pipe without havingto call a plumber).

A welder is the same thing; a tool. No, you won't save four or five hundred dollars on the first thing you weld to justify the purchase price but over time as you fix a lamp here, weld a bike trailer there, and so on; eventually the welder will have paid for itself and then some. I survived for 20+ years without needeing to weld anything but since I've owned a welder I've found at least 1-2 projects a month that were made possible or at least simplified by owning one.

Money spent on a tool is rarely money wasted.