Mishima is one of the closest Shinkansen stops to Tokyo, which makes it deceptively quick to reach - well under an hour on the right train. The choice is the usual Shinkansen-vs-local trade-off of speed against money. Here's how it breaks down.
Kodama trains stop everywhere but are cheaper to reserve and still get you there in under an hour - perfect for such a short hop, so don't pay up for a Hikari unless the timing suits. From the station, the Skywalk is a bus ride, not a walk, so build that in. All fares and times here are estimates - confirm on a transit app.
Take the Tokaido Shinkansen (Kodama or Hikari) from Tokyo Station to Mishima in about 45-60 minutes for roughly ¥4,000-4,500, with no transfers. JR local trains are far cheaper but take around two hours with changes.
Catch a Tokai bus from the south exit of Mishima station - it's about a 25-30 minute ride. The Skywalk isn't within walking distance of the station.