If you want some cheap dice, go for those X times 7 sets on Amazon (they contain a D4, D6, D8, D10, D10%, D12 and D20 per color) and look for as many transprarent colors in the package as possible! "Imperfections" like air bubbles inside the material unbalance a die, but are easily visible in transparent ones and often get tossed!
(Same product on amazon.co.uk,.fr,.it and .es!)
This is a pretty good example on Amazon Germany. 10.99€ for 49 dice? Must be shit! Might be, but this set has only 2 opaque colors. I've bought similar sets twice (35 and 42), and only one transparent die was Crappy McCrapface (had a huge bubble). All other transparent dice were fine. I've tested them all for balance¹, only the one transparent die with the visible bubble was unbalanced, about 15% of my opaque dice were, too.
Both of my packages came with little velvet bags for each color and a large bag for all dice. Even if low quality, they make for a pretty cool little gift!
PSA: "Pound 'o dice" from Chessex - Don't buy!
A friend of mine bought one of those. There's 1 guaranteed full set of 7 dice and the rest is random. He got only two D8 in total. And he got a lot of "pretty" dice, however nearly all are opaque. Half of his opaque dice are unbalanced.
¹ = Warm water, saturate with salt. Die floats, tip and see what number moves to top, if the same number is on top all the time => die is unbalanced