It might make a decent P1/P2 car depending on the size of the engine.  But by the time it would be ready to rally, it would be a $10,000 rally car, and you could probably build/buy a better car for the same or less cost.

There are a few cars for sale that could be good starter cars.  Harry Anderson's Talon is available at a good price (see the Buy and Sell forum), I think Jean-Sebastien Busque's Swift is still for sale (http://www.fourstarmotorsports.com/CatalogData/Classifieds_113.htm down near the bottom of the page), and the RSQ classifieds at http://www.rsq.qc.ca/annonces/liste.php?categorie=1-1 usually have some cars for sale.