An automotive locksmith can help you, and do it much cheaper than an automotive shop, or car dealer. They won't have to tow your car, they can do it on site.
Generally, an electronic car key is well protected from water, but yes, putting the key in the microwave did ruin the chip.
Depending on the make/model and year of your car, the price will vary for key "re-fitting", it is expensive, yes, but not as expensive as your car dealer or mechanic (who will call a locksmith and jack up the price to you).
Be sure to call a reputable locksmith shop, one who had their business in town for years. If you can't find one, check
www.aloa.org to find a reputable locksmith.
Lou ....Professional Locksmith