Answer
$294,968$ dollars.
Work Step by Step
Step 1. Given $a=320,b=510,c=410\ ft$, we have $s=\frac{a+b+c}{2}=620\ ft$
Step 2. Using Heron's Formula, we have the area
$A=\sqrt {s(s-a)(s-b)(s-c)}=\sqrt {620(620-320)(620-510)(620-410)}\approx65,548.5$
Step 3. The total price is $4.5A\approx294,968$ dollars.
