Value depends on the "worth" of your items. The higher the worth - the higher value.
You can check current odds(values) for a bet at the match page.
If you bet on a team where you get the value: "1.5 for 1" - this means if you placed weapons with the sum value of "1" your bet value will be 1.5. So if your bet is successful (i.e your team wins) you'll get your items + the item(s) with value a ~1.5.
The more "value" your bet is worth - the more expensive item you'll get after the win.
E.g. your bet value is: 3.
The system wont give you 30 items with a 0.1 value. The system will try give you one item with a of value ~3 and if there are no items with a value of 3, will give 2.9 + 0.1 or 2.8 + 0.2, etc
The system will always try give you the most expensive item first, instead of multiple smaller items first. So, if you're value is 10, it will first try give you an item worth ~10 and if it can't, it would try give you an item worth +- 9 and an item worth +-1, and so forth.
Values are based roughly on the steam market. Values are generally updated automatically but there are some exception - which means some values might grow or fall slower than it does at the market.
If you bet Socketed items, there's a good chance you won't get the exact item back. We keep track of item names that were placed not specifc items, so you'll get the same item back, but probably not the exact same item you bet.