Is It Redundant To Use "But" Before "Alas"?

It's not redundant to use "but" before "alas" if you want to show a contrast in your writing. For instance, take a look at this title from The New York Times:

She's Lovely, But Alas, She's Only Software.

But you can also use "alas" alone. The New Oxford American Dictionary gives this sentence as an example:

alas, my funds have some limitations.

So, all in all, if you are going to show a contrast in your writing, feel free to use "but" before "alas"; otherwise, you may use "alas" alone.