OK, from looking at the latest pictures (4 of 5 is best..), I'd get a machine shop to
0) remove the old bearing inner race
1) cutoff the damaged threaded section
2) drill into the spindle ,say 1-1.25"
3) tap the hole
4) lightly 'cleanup' the entire shaft. Leave new bearings there ,so they can fit properly.
I'd think $100 would be a fair price for the labour and time.
The bolt only has to hold the pulley on, no real stress, that's what the Woodruff key is for. When assembling, coat bolt well with neverseize,install, remove, dab a little more NS, then final install.
Jay