I do Halloween in a big way. This year, our house is a haunted pumpkin patch and I'm slowly adding pumpkins each day, and just finished turning our garage peak into a giant jack o lantern face and we've got skeletons climbing the tree and will end up with about 6 skeletons wandering around a patch of 30+ pumpkins and blow molds with a custom made pumpkin fence and lots of lights.
Many years I do full size candy bars but this year is going to be fun sized with other popular candy mixed in - we do 3-4 pieces each kid (we give it out, we don't let them grab their own). I usually wait til they start the sales (which is starting up already) and then figure out the cost per ounce of each bag I'm considering and go for the one that is cheapest. I get chocolate for around 19¢/oz and the other candy (usually ends up being Wonka mix of sweet tarts, nerds, bottle caps and laffy taffy) for under 12¢/oz). I usually look for the absolutely largest bags of name brand chocolate/name brand regular for the best pricing. I don't buy candy based off of what exactly is in it - I mean I get name brand mix like this year is Milky Way/Snickers/M&M/Twix/3 Musketeers - but that's because this particular bag was like 96 ounces and around $19.
My best advice? Get candy that isn't your favorite so you don't eat most of it and have to go buy more. I'm not kidding. Took me years to figure that one out... bad for the budget and the waistline. :D
I try to stack discounts. I have a Target card, so that's 5% off every day purchases. Then they run an sale (right now, there's a buy one, get one 50% off on many of their large bagged candy). The husband and I got our flu shots there and Target gives you $5 gift cards for that, so $10 on there too.
But Aldi's candy actually beat the regular sales on Target this year! So I saved the Target gift cards for other needed stuff this year.
Dollar stores are not good deals for candy to hand out. They have stupid small amounts in their bagged candy, and the best way to figure out if it is a good deal is once again price per ounce. Unless you've got a super deal, they're going to be more expensive overall. But they could be nice for small toys if you don't plan on handing out toys to EVERY kid - check out the stickers/tattoos and other little things if you don't want to order online.
And I always get a bag of the cheapy candy to bulk up the offering. Usually it's the PlayTime bags for under $8/70 ounces, and they have dum dums, tootsie rolls, charleston chews and dots. All are still good candy, but that is the cheapest non gross candy we've found.
I do Teal Pumpkin as well. That's the thing about non-food items for kids with allergies. I get toys in bulk throughout the year that work, or I go to Oriental Trading (owned by Berkshire Hathaway!) and order some cute stuff in bulk. I usually do glow bracelets, spider rings, whistles (I scored a super cool vampire lips whistle one year that made a zippy kazoo like sound that was AWESOME and you could hear kids for hours up and down the neighborhood after coming by my house!), oh! SLAP BRACELETS were absolutely a hit last year - OT has Halloween versions too. You can find tubes of glow bracelets in the dollar stores most of the time for 8-10 for $1, or check Michaels or the Target dollar spot sometimes they have them too. I spend about half an hour snapping, shaking and putting them together during the early part of the night before the TOT-ing gets going so I have them all set to go, or else the other stuff I throw into a separate bowl (whistles/slap bracelets) and hold out a few options to each child to allow them to see and pick their own if there are different choices. If we get a mad rush, I hand out the toys while the husband does candy and it usually works out well.