The cheapest way to do this is to connect the output of your tape deck to the analog inputs on your computer's sound card. However, unless you've got a great sound card, you will most likely be dissappointed with the results (I was).
I would suggest you look on ebay for a stand-alone CD-recorder. They all have analog inputs and an internal A/D converter. You should be able to pick one up for about $150. Just avoid the no-name brands. I have heard/used Pioneer, Harman Kardon and Marantz machines - each was fine. Be aware of the feature-set also. For example, I happen to require independant L/R recording level controls, and not all CD recorders have this feature. Unless you are dubbing CDs or making mixed CDs from other CDs, a single-drawer recorder will suffice and save you money. In my experience with a Pioneer CD recorder and a Marantz CD recorder, the CD-Rs are pretty faithful to the original source (just watch your levels!). Note that consumer CD recorders will only record on "Music" CD-Rs (and some on Music CD-RWs), but pro or "pro-sumer" decks, like my Marantz CDR-632, will record on almost any CD-R or CD-RW media. I have had the best results with CD-Rs by Taiyo-Yuden, Fuji and Phillips, which are all very inexpensive if you know where to get them. Different recorders may work better with different brands of media.
Also, note that the life expectancy of CD-R media is typically little more than 10 years. Either retain the analog originals, or (as I do) date your CD-Rs and burn a fresh copy every five years or so. For this purpose, your computer CD-R/RW drive is fine.
