USPS First class has limited tracking. The Customs number can be used to track the item but once overseas, the tracking depends on the local mail service to update status. For more protection, you can register your item for an additional $12. USPS first class has a weight limit of 4 lbs.
I recently mailed something to New Zealand that was in a box, a little over 2 lbs and cost $20 for USPS First Class.
USPS Priority mail is more expensive and really doesn't get the item there much faster. The flat rate options have no tracking or delivery confirmation other than the Customs number.
This is all off the top of my head. I'm sure someone else can give you more info that I missed. HTH!