Well, that's sort of a long story. In the end I paid $350 for it with a new SERO contract. The SERO website,
http://www.sprint.com/sero, doesn't have the 700wx available yet. They do have the 700p for $350, and they had (I just checked and they seem to have removed it) the PPC-6700 for $320. When I signed up for SERO the 700wx wasn't out yet, so I got the PPC-6700. The 700wx came out when I was still in my 30 days, so after calling about 10 different reps I was finally able to get one to exchange the PPC-6700 for the 700wx if I paid the price difference. Most wanted me to exchange it through the Inphonic, the company which distributes the phones for SERO. Since they didn't have it, that was a problem. But if you call enough people you can get it exchanged.
The other way to go about doing it is to just walk into a Sprint store and get the 700wx on a regular plan. Then you can call up Customer Service and pester them until you find a rep willing to let you switch your current plan over to SERO. You may have to call in about 10 times for that as well. Either method should get you a 700wx on SERO eventually though.
You're going to love the 700wx. It's the 700w with all the features, plus more, but none of the bugs. It's in the same shell, and has the same OS, but really feels like a completely different phone. I love it (but not as much as I loved my Q. I can't wait for Sprint to pick the Q up).
Getting back to the topic at hand, the 700wx works great with the Slingbox. I get much better results with Sprint than I did with VZW because I get double the data speed with them than I did with VZW. And I also dont' have to worry about breaking the terms of my contract because Sprint allows streaming.