Reddit reviews The Works of Irving Fisher (The Pickering Masters)

You can buy the collected Works of Irving Fisher, but I suspect it's out of your price range ($1600.00....yes, you read that correctly).

For a more modest sum, you can buy his book, The Theory of Interest, which is considered a classic. Alternatively, it's available free in pdf format here.

All that said, the way economists converse with one another has changed dramatically since Fisher's time. Specifically, we say things in math now that people used to write out in plain language. While that may seem like a good thing to those not versed in math, math has the advantage of being concise and unambiguous, neither of which can be said of language.

All this to say: reading the works of the old masters (like Fisher or Keynes or Bohm-Bawerk) can be a bit of a tedious slog through imprecise, wordy sentences. This problem is compounded by the fact that the jargon has changed a fair amount since then, so you will encounter a variety of terms whose meanings you won't be familiar with.

When you consider that most of those guys' good ideas have long since been incorporated into economics textbooks, in my opinion, you're better off sticking to a textbook unless your motives relate specifically to economic history or the history of economic thought.