You do not have to accept "Express with tracking is required by Paypal".
You have not asked for express delivery and Paypal don't stipulate any criteria for tracking of the parcel,that is set between the seller and the buyer.
The seller should have set the postage costs in the listing,not after it has finished,they are in breach of the code and rules of ebay.
This sounds very much like a postage scam,tell them what i have told you and see what their reply is,they have a LEGAL duty to set an honest
postage,remind them that the listing is LEGALLY BINDING,do the decent thing or they will be reported to ebay and negative feedback will
be left for them,hopefully putting the frighteners on them might work and they do the decent thing.
If they don't act for you,report them and leave negative feedback,the buyer does not have to put up with this intimidation.
Hope this helps,
KTF,
Ron.