If you are indeed close to interchange, you shouldn't have an issue with many of those things (aside from Amex). Cybersource and Authorize.net are a source of your problems - they do their best to lock you in to terrible pricing and tack on hefty fees all over the place.

Foreign fees really should be quite close to your other fees. You take a hit on the fact that they are "foreign" but they actually fall under a lower interchange category, so it comes out a wash for the most part. There should be no float-related costs, gateway fees are standard for auth.net, most reasonable places won't charge you PCI fees if you fill out the simple questionnaire, etc. With a decently-priced interchange plus merchant account and gateway, you should come out much cheaper.

Disclosure: I'm with FeeFighters (http://feefighters.com). We have a bundled merchant account/gateway (http://samurai.feefighters.com) that is a bit different from Stripe, priced at 2.3% + $0.30, but has a monthly fee of $25 and AmEx is separate (2.9%+$0.15).