The best approach is to get a second hand ppc accelerator
it has some advantages:
1-.You can easily turn into RTG with Blizzardvision PPC
graphics card without towering.Also be aware of the cooling.
2-.it can be upgraded to up to 128Mb with 2 simm modules on it.
3-.it also have SCSI controller so you can use
(expensive ones) external SCSI CD- CDRW units also without towering.
the internal controller can be used with two IDE devices
you can connect one ide Hardisk and one ATAPI CD-Rom.
Of course Atapi CDROM not fits into the keyboard.
For that you need a special 2,5" to 3,5" 40 pin ide cable.
All of this can be power hungry and sure you need to modify an
PC power supply to fit your needs.
another option may be (towering is a must in this)
a cheap 030 accelerator with 16 or 32 Mb ram and a mediator PCI
busboard
that enables you the possibility to add such an Video card as
Voodoo 3 3000 up to Voodoo 5 55000 pci,Soundblaster 128 card
ethernet card and Video capture card.Towering in this option is
a must and, unless you are willing to do some cutting/modding
Amiga towers are very expensive.Note that with towering
option you also need an Keyboard adaptor.
Not sure about how expensive/cheap are each option,
maybe someone can explain it better.
Hope this helps