Hi, We just purchased a 2012 20 SLI. Great boat and having a blast. The boat did not come with a depth gauge. After pricing gauges in the 400 to 500 dollar range I thought about just adding a Garmin fishfinder. I'm looking at one in the $100 to 150 range. I'm not sure, do all models come with depth readings as well as water temp readings? Does this seem to be the mose economical way to go?.....any other suggestions?