I Googled your exact question and it gave me several good software solutions on the first 2 pages. So, are you willing to pay for such a solution?
The first I clicked was Papercut. It states:
Automatically route large jobs to more efficient high volume printers.
Second i clicked was Print Evolve Suite:
For instance, IPM can automatically route all monochrome print jobs to a high-speed monochrome printer. It can mandate that multi-page documents be output in duplex mode (a critical capability for companies looking to work “leaner and greener”), or that all e-mail or web page printouts be in economode. It can even prevent certain types of jobs from being printed. On top of that, it requires absolutely no input from the end-user. Automatic notifications are available to make certain that the end-users are informed of changes to their print jobs.
You need to check yourself if this one can handle routing according to number of pages.
Third one was OM Plus from Plus technoligies:
Additionally, print jobs can be automatically re-routed by OM Plus from network printers to a large central printer if they exceed a certain number of pages (or other criteria). At that time, the end user receives an email instructing them how to pick up their re-directed job. This improves throughput by utilizing a higher volume (and usually lower cost) printer.