Biggest question to ask is how is it getting to the water? Vehicle rack? Riding aboard a boat that you are towing? Do you have a lake house and are storing it there?
From there, determine the size you want. Not just where it will fit in transit but what you are willing to carry to the water from there.
I live on a lake and have 2 10' pelican specials from a sporting goods store that I bought at the end of the season on sale for 250-300 each and came with straps and foam pads for the roof of my truck. They serve our needs just fine, but as All Dodge mentioned, they dont come on the boat with us as they are too much to work around, even on the 25 foot pontoon. If they see the water while we are on the boat, it is because my nieces decided to paddle them to the sand bar instead of hopping on the pontoon.
If transportation is an issue, there are now some really well made inflatables that perform on par with the pelicans that I have. That could be an option.
Look for end of season sales or 2nd hand ones from marketplaces online.