One minor correction, it's a 1988 Modulus. The decals are not correct for 1989. In 1989, according to T-Mar, the downtube decal would have an "insert" written right into the last three or four letters of "NISHIKI". Also, the red and white color combination was offered in 1988 in the Modulus model along with the tri-color model that you've seen in pics.
You can find more information in this thread from the C&V forum
http://www.bikeforums.net/showthread...+serial+number
If you want to verify the age of the bike, you can using the two digit date code on your components (I use the derailers). You can decifer using at the vintage trek website.
BTW, a Modulus for $80 is an excellent buy. That bike is easily worth double that around here on CL, maybe $200 in really good condition. So you've got room to invest in new tires etc.