how much is it worth?
Welcome to the forum. I am assuming you are talking about your '98 30' Excella 1000. The simple answer that I'm sure you don't want to hear is, it is worth exactly what someone will pay for it.
However, I would suggest you brouse thru the listings here in the classifieds, all the listings you can find on line at dealers, craigslist, etc., to get an idea what others are asking for simular trailers. The fact is, there is nowhere that I know of to go and get a realistic value for used Airstreams, as NADA is all wrong.