like the above mentioned, you dont need the best of the best. However the above mentioned coilovers, (JIC flta2 and a1us, tein He and Flex, and KTS) are between $1000-$1500, and are all very nice coilovers. The HE maybe the least favored of the bunch b/c of its features. Research all of them and pick from the ones that appeal to you the most.
One coilover you didnt mention is the D2 coilover. Use the search function to learn more about them. They seem to be all the rave among coilovers. i might be sourceing my self a pair, in the near future.
Rather than throwing out anymore misinformation, heres a link that will tell you almost everything you need to know about most every coilover on the market for the 240sx/silvia.
Peep it.....30 moons.com Informative Coilover Comparison