I ran a Novak 10.5, Orion 3800, 78/25 in my losi.
When I was running my 3 year old Scorpion 3200 25c packs with a stock brushed motor it seemed like enough power.
If your looking for a budget set up that means its gonna be for a newbie who will be at the begining of the learning curve for driving and setup so the smaller packs should be fine. If they have full power down the straight that just means there going to spin out in the infield. Your probably going to have a hard time finding anyone who is running smaller packs now because we're all part of the bigger is better crowd.

The Slash class is where its at for newbies. You can't beat it for durability or price. And its fun to watch newbies bounce off each other with them. They realy force people to learn throttle control with the crappy tires.
When my son is old enough to race im sarting him off with a Slash! That might not be for a while but I'm sure my Slash will stil be around.