My suggetion: use all different sizes--- from the Vienna sausage/Beanie Weenie size all the way up to the largest coffee or super-sized green bean cans. Make the arrangements fit the size of can.
To save money: buy the sample sized containers of paint, or try craft paint. (Be sure to read the labels about if it can be used on metals). I think I would keep the paints flat, not satin. Use wild flowers or the flowers blooming in your garden instead of buying artificial. Hosting a big party? Ask friends and family to keep their tin cans for you! Need more than that? Print it in the local newspaper or post it on social networks.
The event: A vintage shower/party, a girl's afternoon lunch, Mother's Day dinner.
My spin: keep the cans metal, but tie them up with beautiful ribbon, rafia, or twine. Pair with a colorful table linen and plates. Also try mod-podgeing (is that a word?) decorative paper to the cans.
Branch out: If you keep the cans metal, the same idea could be used for a western/cowboy party. Group the cans with bandanas, straw, cowboy boots... you get the idea.
Splurge: Hit up antique stores and flea markets for metal cans with the original labels....Add equally colorful flowers to the colorful labeled cans and pair with a simple tablescape.