7 years ago, we got a "deal" at CW, to install one on our 23SS. but ours has a 12' slideout, much longer than your 233S's.
it cost us around $500, with installation. the longer topper put it in a higher price bracket.
there are only two topper manufacturers, Dometic and Carefree. i would check CW since they often have a install price deal quite often.
and Zoe the Wonder Dog(R.I.P.)
'07 Roo 23SS pushing an '07 Chevy Avalanche
Equalizer WDH and Prodigy BC