I was very inspired by that guy who made a MegaMan suit for his son and had all but decided to do a remake when a friend talked me into my second option; a King Koopa suit. Also, I couldn't find anyone who had made (a reasonable-looking) Koopa suit which made it a bit more fun.
There were parts that didn't come out quite as nice as I'd hoped, but on the whole I'm really satisfied.
All in all it took around two weeks of working non-stop in evening and weekends. Cost wasn't that high actually, maybe $50 or so.
Step 1: Materials and tools
To paint and glue the sheet insulation you need water based glue and paint. This is very important since the usual solvents all make the sheet insulation turn into a sticky goo. I used about 5m of fleece fabric and just over a kilo's worth of teddy bear stuffing as well. Oh, and about a meter of velcro.
Okay, I know the pic sucks but I forgot to take a picture of all the stuff and had to settle for what I had left.