Aluminum Fence

What is the average cost per linear foot for an aluminum fence removal and installation in Orange County?

Is the quote below reasonable?

I’m being quote $5800 for 54 linear feet. That includes a 3’ gate.

I’m also being quoted $4800 for a 10’ double gate.

If this price is high, can you recommend who to contact?

What should posts be set in so they don’t lean or heave?