That's about right. Think i paid roughly $500 for a new dexter axle to be welded on my older drift boat trailer by a trailer shop in Ellensburg a couple years ago.
If the spindles were damaged by your wheel when the bearings blew, a new axle is the right answer. When i bought my boat, i had to replace bearings way too frequently on trips as the spindles were damaged. a new axle with fresh spindles fixed it right up and haven't any blow outs since, just preventative repacking of the bearings.