Most computers have a "gauge" mode.
There's simply no way that I'm going to encourage you to purchase
any gear yet, and when you do purchase, the computer will be the last thing that I recommend.
That said, there are three vital pieces of equipment: a depth gauge, a timer, and an SPG. How you choose to package them is up to you, but inside of a metal and glass "computer" on my right wrist (plus the SPG clipped on my left hip) is my favorite way. I believe you'll find that metal and glass is dramatically more durable and readable than anything you'll find made of plastic. Halcyon, Dive Rite, DIR Zone, ScubaPro and the like all make very nice 2" brass and glass SPGs. Avoid the boot, as it serves very little to protect anything, and creates a trap for water to create corrosion. Boots also hide problems that you might see otherwise while rinsing your gear.
There are several stainless and glass computers on the market - my personal favorite is the Suunto D6, which conveniently logs dives (and shows graphical profiles both in it's excellent software with USB connection and right on it's screen). Its face and numbers are bright and large, and the unit includes a very usable compass so you don't need a separate compass (which, in my opinion, is used a lot less than what would justify wearing a separate unit). Of course, the D6 also does temperature, ascent rate, and stopwatch with quite a number of automated features like you mention above. In computer mode, the D6 also shows NDLs... Which is fine, if you choose to use that later once you already know your NDLs pretty intimately. In gauge mode, the display is a lot better and more informative than it is in computer mode, with the display showing more information with a higher degree of accuracy (shows seconds as well as minutes, etc.)
The same software is available in the Vyper, but the Vyper is a much larger unit (meaning that you won't wear it except when diving) without the special display that allows you to see your graphical profiles. The Vyper also isn't metal and glass.
That said, all of the gauges I mention above are fairly pricey units - but then, you get what you pay for. Find an online source - I think I spent about $650 for my D6 delivered to my door. I saw one shop that was selling it for almost three times that price.
...Which is why I don't think you'll get much use out of a $150 computer. It might last you for a couple dozen dives, but I would certainly not consider it a solid purchase - and certainly not the first thing I'd recommend when considering a gear purchase.
If you're strapped for cash and want to go diving, I'd rent a little gear for a few bucks and go diving.
If you HAVE to purchase gear, I'd start with your mask and fins and progress into your exposure protection, which in your case - unfortunately - may be a drysuit. If you do decide to purchase a drysuit, I recommend finding your nearest DUI dealer and scheduling an appointment to be fit properly. My favorite drysuits are the TLS350 "Signature" series suits, which are self-donning and have a telescoping torso. For a few dollars more, you can get one completely custom fit to your exact measurements. I'm also a fan of their heavier-materialed CLX450s, although that's only because I'm diving commercially.
For a really great drysuit, expect to pay something like $3,000, plus or minus based on what sort of features you get.
After you see what goes into making your suit and what sort of service you get with it, you'll understand why they're so expensive.
There are cheaper drysuit solutions on the market, and some of them "aren't bad" - but if you're looking for a truly self-donning suit with a custom fit and a telescoping torso, there's only one solution on the market. All others will be a compromise.
...Which is why I recommend taking the few bucks that you've got and going
diving with it rather than buying
gear with it.