Well, the price for foams are roughly $14-$16/pair. Some are more, I've seen JACO foams that go for $22.
IF you want to mount rubber, it'll cost you about $16/pair + the cost of CA + the cost of a new rim (if you don't reuse the old one). That's fine but then there's the time you put in to mounting them and taking off the old rubber. If you get the premounted rubber tires, cost will very.
If you want to reap the benefits of rubber, you should get the premolded inner foams (soft,medium, medium hard, hard) so you can get a good contact patch off the rubber. These are about $5/pair.
The life of foam will vary depending on use, surface and shore rating. I can go through a set of foams or rubber tires in a day if I drive them hard enough I go through 2-3 sets of foams when I race but that's just based on traction. Afer a day of racing, I'll have 2-3 sets of good bashing tires.
Overall, the traction of foam tires is better than rubber tires. It's all personal preference but after a while, cost effectiveness points to foams. I used to use rubber tires for about a year, then I started racing and foams were the better way to go. I then realized that it was cheaper and more convenient to go with foams.