Small Coin Envelopes to Use for Rice at Wedding?

Instead of making up rice bags with the netting and tying a ribbon around it, I thought maybe we could fill coin envelopes with rice. I plan to put some kind of a decorative sticker on the outside with the bride and groom's name and date or something like that. My question is does anyone know what size coin envelope I should use to allow enough room for the rice. I've seen a couple of sizes

2 1/4 x 3 1/2 or 2 1/2 x 4 1/4 and where can I buy the white envelopes? I find the brown, but the only way I find white is to buy 50 at a time and I need about 350. I wanted to buy a box of about 500 which the brown ones come in. The 50 count of white are way more expensive.

By Brenda Wilson