All matters what you are looking for. Those Omori gauges are ridonkulous in pricing. Electrical or mechanical makes a price difference too; with mechanical being less expensive.
The price your quote seems to be a real cheap price. I got mine for about 45 bucks from NewSouthPerformance. They sold a bundle including the T-fitting (reduces interior noise greatly) and steering column pod. Makes for a very slick install; many passengers assume it is stock.
if you know where to look, vacuum tubing is about US$5-10 for lengths ranging from 3-10 feet.
T-fittings are easy (most hardware stores), but T-fittings with a flow restrictor in them keep VDO gauges from buzzing are a little tough. probably US$3 for one of those from a place lie NewSouthPerf or 42nd Draft Designs.
If you don't like cobbling all of the parts together, definitely get yourself a kit.
well, i got a brand new VDO boost gauge with the tubing already for 15$ on ebay... Didnt instal it yet but looks good! I was lucky, no one bid on it, i was the only one but for 20 shipped with tubing is pretty nice...