As a Mr. Beer starter like you a couple of thoughts
You want a 5 gallon batch, not a 5 gallon carboy, that requires headspace beyond the 5 gallons.
I use wine & beer buckets for my fermenter now.
To start you can buy a kit beer such as brewers best kits, that have 2 cans of extract, but an extra pack of yeast, and split the kit. Two cans make it easy to split.
Don't worry about the difference in size (Mr. Beer being smaller than 2.5 gallons, it's close enough for now)
Your cost should be close to half the cost of using Mr. Beer kits for the same strength beer.
A ROT on equipment, ALWAYS try and buy bigger than you think you need.
A turkey fryer works well as a brew kettle. and you need a chiller, a coil of copper will work fine.