Transferring cassette tapes to CD

Hi,
I have so many cassette tapes that I kept for years. All of these still plays in my CD-Cassette player with good quality sound.
I know that these tapes will not last for a very long time like audio CD’s.
My problem is, how I can transfer songs in Cassette tapes to CDs?
I know that there are shops that offer transferring of music/video from cassette tape to CD, VHS to CD/DVD, but it is too expensive.
Thanks.
