Its not going to be worth a lot, probably only a few hundred for an easy sale. Raleigh made a few tandems in the late 90s to mid teens, being 24sp I'd guess yours is in that age range though I don't remember it in particular. The nicest were the pursuit which was a 27sp road tandem, the disc version of the companion or the Cadent. The rest were largely comfort style for couples to have fun, leisurely rides around town or the local bike path. The disc Companion and Cadent were slightly better equipped versions of these comfort style and used 700c wheels. Other than the Pursuit, they all retailed for 600-1200 and, like many tandems, haven't held their value well. Last year I paid 300 for a 27sp Ultegra/Phil Wood equipped Co-Motion that would have been significantly more than yours when new and is probably about the same vintage and that's cause after 6 months of trying to sell it for 500 the owners just wanted it to move on. But I've also sold 3-4 tandems that, after weeks of trying out didn't fit right, for 300 with no issue. So while I suspect you'll have a hard time getting more than that unless you get lucky, it should be an easy amount to sell it for.