Hey i've recently started using ebay plus. First, keep in mind this is only a promotion and from experience will only last 1-3 months going by other offers ebay put forward in the past. 

Secondly, I haven't sold anything yet through ebay plus + express. You have to add the cost of the express postage SEPERATELY therefore the buyer will pay for the additional postage costs. 

Also, try sending these $2:20 items in an express post envelope as merchandise which costs around $8 (C5). So you are out of pocket under $6 - and you can charge $6 for this - and ebay you will give you $4 back - and you profit $4 until the promotion ends.