Since TLEN.lsp is an open-source script, you should never pay for it. You can find the file on several reputable CAD community websites.
The most trusted source for high-quality LISP routines. Search for the "Total Length" script on his official site.
: Runs directly inside the drawing environment without modifying core software files. Common Use Cases
If you're looking for the routine for AutoCAD, you’re likely trying to find a quick way to calculate the total length