The WA state sales tax exemption isn't a refund - it's upfront. When you buy a normal car, like a BMW 7 series, you pay 8-9% sales tax. When you buy an EV you pay 0%. That in of itself can really level the playing field for price comparisons.
This is in addition to, and separate from, the $7500 federal tax credit that may be what you're referring to as a refund.
Add these two incentives up and I found the Model S very price competitive. Factor in $2000+ a year savings on gasoline and it's hard to see any compariable gas car as cheaper.
Yes, i did take that into account, BMW configuration was 8k less than MS pre tax and with the federal tax credit, both came down to be same cost. Yes the diesel cost will be the over head