Yep, the Barney show is still running, but it's at Universal Studios, so that's a whole different park you'd have to buy tickets for. Although on a tight budget, the Universal parks are quite a deal right now. You can get 4 day tickets for $99 and get a free child's ticket with each adult. So you could get 4 day tickets for all of your family for $300. Although if I had to choose between WDW and Universal, I'd definitely pick WDW.
I just checked undercovertourist to see if they had any good prices on 2 day tickets for WDW and they are actually more expensive than getting them direct from WDW (although shipping is free).
So here are the best prices I know of (including tax):
2-day tickets (from WDW):
Adult: $133, child: $109
Total: $726
3-day tickets (from Ticketmania with Mousesavers rates):
Adult: $190, child: $156
Total: $1038
4-day (Ticketmania w/MS rate):
Adult: $200, child: $163
Total: $1089
5-day (Ticketmania w/MS rate):
Adult: $200, child: $161
Total: $1083 (yep, cheaper than 4-day tickets)
So the jump from 2-day tickets to 3 is pretty substantial, but after that, it's not much more to go 4 or 5 days. I certainly understand being on a budget, but if there's any way you can swing it, the price of 5 day tickets is quite a deal compared to 2 days. If money wasn't an issue, I'd think 4 days at the parks during a 7 day stay would be perfect. You could do 2 park days, then a rest day, then 2 more park days.
But if you have to limit it to 2 parks, my vote would be for Disney-MGM Studios. It has 2 of the best rides in Disney (Tower of Terror and Rock n Roller Coaster), some great shows (Indiana Jones and Lights, Motors, Action and Beauty and the Beast), and my favorite nighttime show (Fantasmic). I also love the movie studio themeing.