The best time to go to Magic Mountain is in October, the last week they are open during the weekdays (the week of Halloween) on that Monday, Tuesday, or Wednesday.
You can replace the hybrid battery pack for $600â$2000. It will be more expensive to do it at the Toyota dealer, and the model of the car also affects price. I have had 3 Priuses in my family, and only had to replace one battery pack (200,000+ miles). I ordered a replacement battery pack from a rebuilder and had it shipped to my mechanic, who had no problems changing things out. The total cost was $1200, back in 2011.
If for some reason you do need to replace the hybrid battery out of warranty, do note that your Toyota dealer should offer you a $200 rebate/bounty on it, so that it gets properly recycled. Used Prius hybrid battery packs (such as from wrecked vehicles) have been selling for less than US$1000 on eBay.