I've got a chariot (a bit spendy) that I adore. It has great storage in the back, has many attachments available (including for cross country skiing and a sling for babies), has air filled tires, etc. My friend has a cheap one that didn't hold up well. Another friend also has a cheap one that seems to have held up well to lots of cycling. However, it's much heavier than mine, it doesn't have air wheels, which is less comfortable for the little ones, and it doesn't fold up easily. I can push a few buttons on mine and stick it in my car. She has to use a pick up to take it places. The Chariot also attaches to the bike with a ball joint, so I imagine it wouldn't flip over if I did. The down side to that is you need to buy the piece that attaches to your bike, so you can't hook it on to just any bike without moving the attachment (easy to do, tho). Also, the cheaper ones seem to have the jogging wheel that stays with the stroller. I didn't use the jogging wheel with my bike, but it doesn't look like it can be used when the bike is used. So if you go for a bike ride and then want to stroller around town, you have to put on the attachment. I'm not sure about this, but I would definitely look at that feature if you want to use it for both purposes on one trip.
When the babies are done with it, my friend is going to use hers for her dog. Her cheapo has a hard bottom. I imagine that would be better for a dog than my cloth bottom one.
All of them, expensive and cheap, seem to have different aerodynamics. I imagine the insides either have different capacity or different angles for the seat. I didn't really check into that, but you might want to. My daughter complains with the chariot that there is no space to put her head back with the helmet, and it is uncomfortable.
The Chariot can hold 80 lbs, I think (it's a double). I don't know about the cheaper ones. My daughter is 5 and just under 40 lbs, so lucky me - I can carry 2 5 year olds in it.
Hope this gives you some things to consider when making your decision.