I bought raw sausages packaged in a meat tray with plastic wrap. The wrapping was taut so that it almost looked like there was extra air in the package. How does one know if this means a swollen package or just wrapped too tightly? It's a grey area but a swollen package worries me. They smell fine and are cooking and within three days of the expiry date and weren't left out of the fridge other than shopping.
If you can tell us, "They smell fine" then you have since opened the package. It is not uncommon for air to be trapped in those plastic wrap trays. Since we can't see or smell it the only way to answer your question is: "Is $4.00 worth of sausage worth a few extra trips to the bathroom?" If it smells 'ok' then it is unlikely to be 'dangerous' ... but only you can make that call.