Car rental, private plane, Uber, lyft
Take bus 574 to Tacoma Dome. It leave SeaTac roughly every 20 minutes in afternoon/peak times. It is about an 80 minute ride for $3.25 or $1 65 and older. I use this mode semi-frequently. Suggest no more than 1 bag. Or drive yourself and pay parking at one of the off airport lots. Coupons are available most place and discounts for military or AAA
Rent a u-haul van! Cheapest! Just the white side panel. $19.99 or a home depot truck/flat. Why pay $100 for a rental car if you're the one driving. Hey, at least you can have a traveling party in the back.
Take the tram. It's. Cheap and fast, although you may need to take a bus or paid ride from where train stops to where your destination in Tacoma is. https://en.m.wikipedia.org/wiki/Line_1_(Sound_Transit)
There's also a tram that will take you to tacoma
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