wow, I didn't know CC made Sport Nautys in '89. What was the first year they did?
I've got a '92 Sport and am in the same position as you. Faded interior. I've been planning it out for a winter project, mostly going to do it myself. For the hard parts like the captains chairs I'm going to contract it out but for the front and side cushions all you need to do is buy some vinyl and staple it down. From what I've been told if you go through a shop they will charge you a lot for the vinyl but if you order it yourself you can get it much cheaper. Here's a list of rockford's marine vinyl.
http://www.rochfordsupply.com/product_listing.asp_Q_CatID_E_419_A_SubCatID_E_489 I've conversed with the this guy and gotten a lot of advice.
http://forums.wakeboarder.com/viewtopic.php?t=22478 I've debated whether I should make a playpen area up there with a spot to put a sack. Wouldn't cost too much extra and wouldn't be too hard. Also maybe converting the backseat into a sundeck with a sack underneath it so I don't have to worry about sacks on the floor. Would be easier to upholster but I'd have to buy new foam for that.
Anyway if you're a DIYer that might be an option. I'm planning on having mine finished by January without doing any sewing on my part.