I tried to get this problem fixed a few months back, whereby I accidentally paid over 600M for 129 x X5 Enduring stasis webifiers: Fix market sell price mechanics
Got a CSM member attention, but this stalled as someone jumped in the conversation and sadly got him frustrated, so he gave up.
But basically you don’t pay the lowest available sell price, you pay the actual amount you punch in. So if that happens way above the market price, you’re screwed. You get a warning the first time you place an order, but not when you adjust it. So a typo can cost you your entire wallet.