Looking for a rot-resistant wood species cheaper than red cedar.

Project is a multi-room shed (maybe 16' square). We'd like to do vertical tongue&groove sheathing to match the house. Like the subject says, red cedar price is crazy and I'm looking for alternatives. Looking for experience and (positive/negative) recommendations.

For example: any one used the "thermally modified" ash siding? Any used red grandis (a eucalyptus species)?