I was in Party City today (Research Forest and I45) and saw that they had a variety of birthday balloons priced at $0.93-0.99 cents blown up. Also, their regular solid color latex balloons were 0.79 blown up. You can get a clip for $0.19 to hold the balloons together. I also overheard that you get 2 balloons free when you buy a dozen of the latex balloons at $7.99. Non solid color latex balloons were $0.89 and a dozen would be $8.99.
This beats the $1 store's deal of $1/mylar balloon. I suppose it comes down to which is closer to you, since the dollar store is on rayford/sawdust behind Wendy's.