The bolts at Tractor Supply range from roughly $3 a pound for grade 2,to $4-$6 for grade 5 or 8 bolts..
And yeah,metric bolts are a pain in the a$$..most hardware or box stores stock only a few in the drawers,not in bulk,and never seem to have the pitch or length I need,or enough of them,and it's always a hike to the only hardware store in the next town over that has a very large selection of them--they know your boned as far as getting any elsewhere,so they charge accordingly..
If you strike out there,then you have to go further to a Fastenal store,and hope they'll sell you anything,I heard some only cater to businesses here and unless you have a "business" and apply for a account there,have a tax #,your likely to be sent away empty handed..
W.W. Grainger had a similar policy and now they don't have a store in the industrial park 5 miles away any more,probably lost a lot of business being snobby as far as who they will sell too..
The few things I bought there,I had to use someone else's account and pay cash to get anything there,and they looked at me like I was lying when I showed them the letterhead from the business a friend had to prove I had "permission" to buy stuff there..
It's too bad because they do have some decent quality stuff like Dayton winches,motors,and they were about the last place local you could buy things like pulleys,key stock,bearings,pillow blocks and other similar items from..now the nearest one is 22 miles away..