The DCE Viper 530 / eMatrix 530 is without a doubt the best accelerator for A500.
030@50MHz
68882@50MHz
128Mbyte RAM
IDE
SCSI II
However they are very rare and I've never seen one for sale on eBay in 10+ years and believe me I've been watching.
If one ever came up I would imagine it would go for silly money (£500+)
