Some of these replies are making this sound harder than it seems.

Here's a tape recorder, it's $25.

https://www.amazon.com/Jensen-MCR-100SB-Portable-Microphone-Limited/dp/B00UY8QEGW/ref=sr_1_3

You could use the microphone, but I'd just plug whatever audio source you have into it. If your source is a laptop, use a standard 1/8" audio cable from the laptop's speaker port into the recorder's microphone/input port.

Then you just need some blank tapes. 2 Pk on Amazon for $5.

https://www.amazon.com/Maxell-108527-Flat-Packs/dp/B000001OKK/ref=sr_1_4

$30 and you're done. Simple as that.

It’s this one Jensen Portable Cassette Player and Recorder - AC-DC https://www.amazon.com/dp/B00UY8QEGW/ref=cm_sw_r_cp_api_glt_fabc_E0QQPYZT13T59AXN6BZ2?_encoding=UTF8&psc=1

Just wondering if something like this could convert mp3 to a cassette tape. I assume so since most things go vice versa but idk.

Not in this case. A lot of hand-held cassette players are play-only. They don't record.

I expect you're engaging in overkill looking to a "converter". You don't need a USB connector or custom software. Just run a stereo mini jack from the headphone jack on your computer to the input of any cassette player with a recording head. (lo-fi example)

Though, why do you want to transfer things to cassettes anyway? Most of the time you'd be better off with a portable MP3 player and a cassette-deck adapter.