98 Intrigue

I have a 1998 Olds Intrigue with less than 95,000 miles. The external air temp. sensor always reads lower than actual temperature. Occasionally it wil drop to lower than 37F and the air conditioner will then shut down. If we wait long enough, the temp will come back up and once it is above 40F the air conditioner restarts. I don’t want to spend $600 to have the dealer fix the issue. Any cheaper suggestions out there?