Assuming the batteries need total replacement every six hundred cycles[0] and the cost of new batteries is $75k[1], that's $0.25/mile; plus charging costs which is claimed to be 2kWh/mile, and that is going to vary a lot depending on when and where you are but the average I generally see for the USA is $0.10/kWh for domestic and $0.07 for industrial supply (and for a semi I think industrial is the relevant number), which means $0.14/mile; the total is therefore $0.39/mile.

A quick google (because I'm not a trucker) suggests the gross fuel expenses of a truck are $0.40-$0.55/mile.

Thus electric is cheaper, with the usual caveats for extrapolation from the sales blurb from a single model vs. the empirical observations of the actually existing alternative. As none of the voluminous criticism I've seen and read of Tesla is about the fuel efficiency being over-optimistic, I'm willing to believe them on this.

[0] the worst claim I found with a quick google was 50% capacity at 600, the best claim was a factor of ten better; the servicing probably isn't going to be free, but a 50% capacity battery is still useful for fixed installations so I'm going to assume that's a wash.

[1] 500 mile range model $180k, 300 mile range model $150k, so extra 200 miles cost $30k, so 500 mile peak capacity costs $30k/200*500 = $75k