Is there much of a demand for audiobooks on cassette tapes? I have a few and wonder if I should post them.  

They aren't as in demand as they used to be. But some are WL because they either haven't been released in CD/MP3 yet or those are all WL and people with cassette players in their car will take whatever comes first. 

I use a lot of audios and have a cassette player in my car. But I still prefer the CDs because I can only listen to cassettes in my car.  Takes too long to finish the book unless I have a road trip.  The new car I ordered doesn't have a cassette player.

I would post them and see what happens.  If they aren't ordered in a few wks or a month and you want them out of the house-then delete them.

If you don't want to go through the trouble of listing them all. You could offer a deal on them.  Figure out how many you can fit in a small box and what the postage would be. Then offer a deal on them in the book bazaar. Just post some of them for people to order and then list the others in the thread as freebies.

I request a lot of audio books on tape for my mother in law, who is legally blind.  She tells me thats books on tape are easier for her to manage.  She's had the tape player for years and so has the controls, etc memorized, whereas CD players are harder for her to use.  

I had 1300 audio books on cassette and put them on my bookshelf. By last year, no one was ordering so I sold them all and went to CD's. When cassettes were popular it was the best way to trade on PBS. They were light so media mail was cheap and you get two credits for them. Also Friends of Library sales have been selling them for 25 cents or 50 cents so they were easy to get. Now,  Audio CD's at library sales are going for $1.00 or $2.00 !!

I find the cassettes at Goodwill and I have ordered a few from PBS. My school bus has a tape player and I have a lot of dead head time. My problem is the tapes are getting old and they don't always play well. I have kept my favorites ,but I did delete them from my shelf. I have a coverter to play CD's through the tape player and so I have begun to go in that direction. If you miss  a word or two on tape, it is easy to go back---on CD you have to go back the whole track>bummer.

I have a mix of vehicles - 1 with only a cassette player, I with only a CD player, 1 with both, 1 with no player.

I decided that I tend to prefer the cassettes because there are many more of them available on PBS, where as most CDs (at least of up-to-date, popular books) are WL'd, so there's a wait.

And as mentioned before, you can rewind a cassette - if I get distracted by driving, it's easy to go back and listen again.  Or if I want to switch vehicles, it's possible to start the book in the same spot with a cassette, compared to listening to a whole track on a CD to find my place.

What I did for my newer vehicle and the playerless one - I went to the local thrift store and bought a $2 portable player.  I keep it in a canvas shopping bag with some extra batteries and move it from car to car easily.  I just sit it next to me in the passenger seat and I'm good to go.  And for those who don't have a cassette player in the house, you could do the same thing, except you could plug it in and save batteries.  And since it is portable - if you want to use batteries, you can move it around the house with you as you go from room to room and not keep missing parts because you are too far away to hear.

If I was listening to music, the sound quality would be an issue, but I haven't found there to be as much of a difference listening to a voice on cassette.

I could have gone the opposite way and used my portable CD player, in the appropriate vehicle, but I find it much harder to operate while driving (switching discs, etc. - and again, if  you don't pause it and leave the machine on while parked and running an errand, (which uses up the batteries faster) you lose your place (at least on my portable) and have to start the track over.

And another reason to chose cassettes is that because so many people don't have players anymore; they want to move the cassettes from their shelves and are more open to a deal for multiples - I've never come across a deal for CDs.

Just my 2 cents. :)

I don't know how fast you go through batteries, but I bought an 'inverter' for my car.  It cost about $20; plugs into the 12v outlet (you know, used to be cigarette lighter) and power is inverted to 110, and your player plugs into a receptacle just like the ones at home.  Mine has 2 standard receptacles, & USB port.  It has easily paid for itself in battery expense.