The dags you mean; they're cut and shaped to fit, then riveted onto/under a matching leather piece. Like I said previously, you want quality, you have to pay for it.
I went the cheap-o route, a lot of us did at one point and we've all come to the same conclusion- off the rack armor just doesn't cut it.
I've had cheap butted mail and experienced ring loss after the first faire season; bought a 'small' sized breast and back plate on eBay for less than $100 - it fit like it was made for a man much shorter and much fatter than me.
When it comes to hard armor, unless it was made specifically for you, you're just not going to be happy with it...something's not going to be right. Even something so small as a 1/4 or 1/2 inch in difference can cause armor bites or leave you exposed.
You might give making your own a try...you can acquire the sheet metal and cut it to the shapes as outlined by the sites Sir Gerard posted. I know Mad Matt sells his CoP instruction kit for like $10.