Car fan motors are a popular and cheap way of getting a good deal of power from your spinner. While you don't necessarily know the condition of the motor (especially if its salvaged from an old rustbucket) the low cost means its no major loss if it turns out to be pish. I've been impressed with the Mondeo car fan motors Tony has used in Drangonstrike and Kishar, and I believe the motors from Jaguars tend to be pretty good too (similar if not identical to the popular EV warrior motors that used to be available).

For a little bit more money, but some very good reliability, I'd recommend the Speed 900 electric motors. I use one to spin a 4.2kg drum on Drumroll and it takes some abuse, keeps on going, and also reaches top speed pretty quickly. There was talk a while back of these motors being discontinued but I'm not sure what the current situation is with that as they are still seemingly readily available.
I bought mine from:
http://quantrum.co.uk/redbankmodels/...-bb-p-759.html
where they're about £30 including postage. They come with a faceplate too that offers an easy form of mounting to a chassis, although the material seems a bit brittle as two of my mounting points sheared at the UK champs.
Overvolt the Speed 900s and you can get an impressive performance out of them.

Then of course, there is the Magmotor (as demonstrated effectively by Hornet 2 ) but that's going well over the 'reasonable priced' aspect of your criteria.

Brushless motors pack an amazing amount of power for their size and weight and 360 has shown how effective they can be, but in my personal opinion, they still need some arena time to prove their credentials. I've kindly been donated one for Drumroll and will hopefully be running it at the tag champs, where I'll be monitoring its performance and seeing how it compares in terms of reliability to the current Speed 900 setup.

Hope that helps a bit