You can get high speed dubbing cassette players, even ones designed for the job, but you could likely re-buy your collection for the cost of the hardware.
There is also no real escaping the loss in quality you would get from high speed dubbed material, I suspect you would be pretty unhappy with the results. Even in dual-cassette players with a high speed dub option, the results were marginal at best, from analog to digitial there might be some clean up you could do but that would take longer than just taping well from normal speeds.
What I did was use one of my old PC's, my cassette player and over time just kept slapping slapping in cassettes, my cassette at least plays either side without having to flip the tape so I could get a whole tape at a time.
We made it sort of a family thing, I showed everyone how to kick one off, and so the wife and kids would slap in cassettes when they felt like it, same as me, about a year later I was done.
If you do find another solution please post it, I am sure a lot of folks would like to get out of their cassettes, but then again, that nothing is readily on the market to do this and there is no lack of consumers for such a product, it gives you a pretty good idea that you will not see anything soon...