About five years ago, I sold a mint 50mm EL Nikkor on eBay, and was disappointed because it went for very cheap. About a year ago, I picked up an Oly XA with flash at a yard sale for $5. The flash didn't work, but the XA works just fine. I knew about the collectible status of the XA and was again rather disappointed to find that they sold on eBay often for very little. If you go to eBay, do a search on "olympus xa" and then click on "completed listings," you'll see what I'm talking about. What I'm getting at is chances are good you will be able to afford both the XA and the enlarging lens without overtaxing your budget.
Best,
Michael