If you're still paying $70 for it, then something isn't right. I got a starter pack for my younger cousin and it was 49.99. A 3 pack of figures is about $30 and a single figure cost $13. Those were the prices I paid for mine when they were first released. The prices may have gone down for the older packs. The starter pack comes with Spyro (magic), Trigger Happy (tech), and Gill Grunt (water). You will need 5 more characters withe elements air, fire, earth, life, and undead to complete the game 100%.If you can buy it somewhere it's cheaper, you would probably spend around $80-90. Again, I'm not too sure about the prices for the figures as I bought mine when they were first released.
The game length is dependant on how much you like to explore in the game. It could be several hours. Of course, they also have adventure packs that come with an exclusive character, a toy that unlocks a new location , and two magic items. There are 4 of those. So I guess gameplay length can also depend on if you're convinced after playing whether or not it's worth it to extend the initial play through.