That sounds very fair to me. Depending on usage I would expect 60k-100k out of the shocks and the springs will probably outlast your T4R. If you're a very demanding driver then the springs may have only 90k of life left for you. (Good quality springs retain properties for 100k or better typically.)
I'd offer him $375 and see if he'll bite. If not I'd pay $400 if that's everything; taxes, shipping everything!