Bringing the fun back into audio - cheap CD tweaks

Should've added IMHO since maybe spending money is fun.
Cheapest would be to handle the CDs carefully and to put them back into the jewel-case after the listening session. Don't let your non-audiophile friends to handle them carelessly $0.
Advantage is scratch-free CDs and jewel cases.
There are a lot of high quality equalizers for sale for almost nothing, including parametrics and those with "pink noise" generators with mics for system analization. The better units allow you to shut down the eq and just let the signal pass through with very little impact on it. Even come with convenient remotes so you can "play" from your seat. Check out the specs to see that the better units introduce very little distortion or coloration relative to the much improved sound you can achieve from many of your CDs (especially many of those from 70s thru mid-90s I've found). I set mine up so that I can easily totally bypass it when I get into serious vinyl or SACD listening by simply moving a couple of cables around.