Yeah, both at fault here... his comms were poor/non existent but your approach was to aggressive (at to early a stage).
If he has quoted $20 for shipping he should stick to that. If he cannot be bothered to find out costs before quote, then that is his affair. Equally, upping the ante and requesting faster post because of the three day delay seems odd.
Do you really need the mech that quickly?
At this stage, I would suggest another email suggesting that perhaps you have been a little quick to register a complaint, offer to remove it and stick to your guns on the $20 P&P. Hopefully if this is written in a sympathetic manner, you might see your mech (which is the most important thing here).
Not trying to teach you to suck eggs here - just saying what i would do...