A bracket with platform like mine is near $1500 you can get one with out the swim platform for around $800
http://www.stainlessmarine.com/single.html
I did the fiberglass myself and it was pretty easy!! But I had got a price of around $700 if they did not run into any problems?? Like a rotted transom.
As for te space were the I/O was I have added a 25 gal gas tank to mine to give me 65 gal total now.
The cover is a nice bait station and sit and jig place also!!
$1500 + $700=$2200 unless you went with the cheaper bracket which would be more like $800 making it more like $1600
But look around for a bracket in your local paper, want advertiser, trader, and local mariner for a take off!! There are lots around for a fraction of the price!