Internal HD Mini SAS to 4XSATA Cable,1.6ft SFF-8643 Host to 4X SATA Target Cable Compatible with Raid Controller Hard Drive

If you're in Canada, the 4xSATA cables are only $17 each. Wire all 20 to a cheap Expander (sample config). Then you only need to run one or two external SAS cables back to one or two ports on a discount external HBA.