I know this is an old thread, but some tips.
Portable cassette players and the like are going to be more prone to have lower quality playback than higher grade component stereo type equipment. The "wow and flutter" specs and "signal to noise ratio" levels are going to be pretty poor.
Put another way, players not even equipped with line out jacks may not be the best choice here.
But being essentially obsolete, you may find your options are pretty limited. You might try a thrift store or pawn shop etc.
A couple of years ago I tried to digitize some old practice and demo tapes. Even a high end cassette deck had very noticeable rumble from the motor, and the common tape hiss, and the result was a let down. Some could be somewhat repaired, but the entire project just wasn't worth the time and effort and I decided it was time to let it go. The technology is way obsolete for a reason....I
I have a whole stack of old gear here I can't hardly give away!