A 68020 is a 68030 that is missing its tiny 256 byte datacache. So there is no logical reason for it to be cheaper. It costs the same amount of money to make an 020 as an 030 for decades.
You're forgetting that '030s can be clocked twice as high as '020s
But if someone wants to sell him an old used cheap one for $5.00 with onboard ram then sure its a good deal then. 
I would even go as high as $7.00 or $8.00 possibly.
You know that's not going to happen. A 28 Mhz '020 accelerator is worth MUCH more than that, and is actually a fine accelerator.
Only when the data has already been cached though, otherwise it's just as slow. It's only got 256 bytes of data cache & most software will have a larger working set than that.
Indeed.
For 3D gaming the 030 is better than 020. For example the framerate in Stunt Car Racer is better. Amiga has hundreds of 3D games that benefit from every ounce of faster CPU power.
Undoubtedly, but I don't think the frame rate is much higher on an '030 that's clocked the same. Seeing how '020 accelerators used to be cheaper than '030s, they're still not bad.
256 bytes datacache is tiny, puny and pathetic but its still infinity times better than 0 bytes datacache on 000, 010, 020.
It's indeed way too small. Too small to be of much use in many situations, and lack of such a small data cache isn't infinitely worse than having one. It would be different if it was, say, 4K.
