[Manuel_D]

MANPADs are still way cheaper than the aircraft they shoot down. You're also shooting a lot more shells to down an aircraft than missiles. On the order of thousands.

Most short range air defenses are infrared guided, radar cross section is not relevant there.

[ryao]

They do not often shoot down A-10s. Also, they are big and bulky, so troops cannot carry very many of them. If you want to reason about this, you would need to know how many MANPADs are fired per A-10 downing. I imagine it is quite a large number.