1、各公司不一样，可以点下一步到付款时可以看到所有费用。
2、加州的法律规定的是8岁以下或体重高于xx磅，内华达是6岁以下或体重低于60磅，都需要安全座椅。租车公司可以租。某些租车公司可以免费提供，沃尔玛也有卖的，大约60刀左右。租车时可以综合考虑。下面有段阅读理解，可以自己看看：
All the major rental companies offer child seats for rent at their locations. It's a great source of revenue for them, because they can rent a $60 child seat hundreds and hundreds of times for $10-$15 per day. It doesn't take a math whiz to figure out that this is a high margin item for them.
There is one secret weapon in avoiding the charge however. Most people don't know that AAA members get one free car seat when renting from Hertz. Hertz is the only company that currently works with AAA, and you must book using the AAA discount code 1805452. (You can enter in discount codes right on the AutoSlash homepage.) On a one week rental, this can add up to over $80 in savings. Even if the Hertz rate is higher than other companies (AAA discount code can bring the cost down significantly), the savings on the car seat alone may more than make up for the difference.
摘自：https://www.autoslash.com/blog-and-tips/posts/how-to-avoid-paying-for-car-rental-options
3、租车需要买责任险（类似于国内的第三者责任险，包括第三者人员和财产损失），碰撞险CDW则赔盗抢和因自己原因导致的车损，责任险必须买。可以看看这个网站http://www.rentalcars.com/类似于去哪儿，给你列出各个租车公司的报价，方便您比较。一些信用卡包含了CDW，所以可以不用买CDW，且一般信用卡公司给的CDW没有较高的免赔额，具体请询问您所在的信用卡。此外，如果在美国有当地的朋友，且有costco的会员卡，可以通过costco网站租车，更实惠。


补充说明：
美国很多地方都没有网络信号，所以一定要租或带一个导航，不要用手机导航，也不要买随身wifi（也是用的手机信号联网）。