in Kijiji, the box spring is so cheap.

The last time I bought a mattress, the delivery guys also had the box spring with them. I told them I didn't want it as my present one was fine. They told me to take it and they would take my old one as they were taking the new one to the dump/recycling.
Seems they are pretty cheap to make and not everyone bothers with them. Especially if they have to haul the new mattress home themselves.

Free bed bugs. You get what you pay for in this case.

Box springs are cheap. My last mattress I bought was being sold as a mattress+box spring. I have a slate bed frame so told them I don't need the box spring and it only lowered my price by around $75.

Bed bugs are free too.

Your savings will be wiped out if this is the case

Box Springs are boxes that your bed sits on. Thats it.

Its a marketing trick they invented back in the day to get more money from customers. Any board, or slated bed frame will do the same. So unless you want your mattress to be higher, its a waste buying a box spring

Get a frame that has drawers for storage under the bed. Way more useful than box spring