I've only seen Eureka in person once. It was pretty darn cool (and tiny :-). Having it and 315 work alongside each other would be great. Of course, painting Eureka to look like a Rio Grande 4-4-0 would be the icing on the cake, but even without that, I'd come up with a thousand dollars for a few days of photo trips and coach rides.
Thinking about Eureka and 315 reminds me that I've always wondered if the D&S and C&TS could work a deal to send 463 to Durango for a month of K-27 and K-28 goodness. Then the D&S return the favor by sending a k-28 to Chama and run for a month there. 1920's sensory overload for sure. Another 2,000 dollars weaseled out of my budget to support history in action.
Having Eureka on both railroads to work the passenger/chase trains would make for spectacular photos. Toss in 315 to doublehead an early San Juan with Eureka and four decent looking coaches and you get 1880/1890 history in action.
Even in this economy, I'd think Dan, D&S, and C&TS could rake in big bucks for such stuff.