There is no way the pricing is justifiable with the cost of components etc.
If priced in sensibly they would sell a larger volume rather than try to mod old kit.
I think it was Motorola that said, Once a product was worked on the MTBF went down by a significant factor.
But keep thinking just because it's aircraft it costs & it is quality equipment
Not quite comparable but marine equipment is peanuts in comparison.
Land mobile equipment also.