My boat is a 14' Aluminum V bottom Lowe jon type. It came with a 15HP tiller, trailer and three chairs for $1,300. I found it on craigslist.org. As far as start up costs: You have to consider taxes and title fees (depending on state laws). Here in PA I paid $280.00 in taxes and fees to make the boat and trailer legal. Other costs were making provision to pull the thing. At the time of purchase I didn't realize my trucks wiring was all crapped out. So I ended up getting a hitch installed on my car instead to pull the very light boat, that was $195.00. Again states vary as to safety equipment; but life jackets for three (my self, my wife, and the 2 year old son) $80.00, An anchor $20.00, fire extinguisher $8.00, whistle $3.00... You get the idea things begin to add up and most of these are legally neccessary to launch a boat. Things that were optional like lights for night fishing ~$50.00
As far as upgrades for the future:
I plan on a decent fish finder one day ~$150.00
Better trolling motor (mine is from the 60's) ~$150.00
I am currently working on front and rear casting decks and some telescoping seats on them. ~$125.00
But I am so glad personally I bought the cheaper boat and upgrading things as I go, because I am using the boat while I am working on it, as opposed to waiting to find a fully loaded fishing boat I would still be waiting and looking and in the end spend roughly the same as I am now.