I bought bags of rice in 5 and 10 lb bags and threw them in an old duffle bag. Worked pretty good until the bags started to break down and little grains of rice would go flying everywhere while I hefted the bag around.
I used bags of brown sugar for awhile too but my kids figured that out and broke into them for a snack and then I had a mess.
So here is my solution. Take the bag of rice
and a roll of duct tape
wrap the bag of rice in the duct tape.
Until it looks like this
Here are all my bags, one ten and two 5 pound bags
Put them in an old duffel bag you have, I had several laying around.
I also found it helpful to wrap some around the outside of the bag to help make it easier to handle.
(Don't mind the small girl child about to climb the dresser in the background.)
and finally use it while working out.
Here is a small cost breakdown
5 lb bag of rice about $4 x2 = 8
10 lb bag of rice $7
1 roll of duct tape $4
old bag laying around the house $0
Total cost is less than $20
Amount of money saved $100!
Working out and feeling great..Priceless!