It'd be easier with a sewing machine... would seriously take me only half an hour to make, they'd be fairly crude but that'd be all you'd need for the sevens anyway. I've got some purpleish denim I was given here so if you don't mind that colour and could pay postage I can whip you up a pair (I'd just make them oversized with adjustable straps). If you're fussy about colour it'd cost maybe $30 to go get some denim (or you could probably get by on about $10 if they don't have to be denim).
Otherwise the easiest way to do it without a sewing machine would be:
- Find some massive denim-look pants in an op shop (pref with an elasticated waist rather than a fly front - old lady style, my MIL has some

).
- Cut off the bottoms so they're the right length for you, then cut one of the bits you cut off open down the leg seam to give you a rough rectangle.
- Tack the rectangle to the front of the trousers to make a 'bib'
- Cut slits (like wide buttonholes) in the top corners of the bib
- Cut the bit from the other leg into strips for the straps, you'll probably need to tack them end on end to make them long enough
- Attach two straps to the back of the pants, one above each cheek IYGWIM
- pull the pants on, cross the straps over at the back, tie the ends through the slits and hey presto, bib overalls
warning, don't google "bib overalls" "old pants" "how to" (I tried to see if anyone had posted a tutorial for you), must be a lot of grotty old men in america with hillbilly fantasies