Fish only with live rock is typically the beginner way to go. I'd go with 1.5 lbs per gallon of live rock. The way I did it was to buy mostly the base rock with a few decorative rocks put in there. Base is generally around $4.99/lb at the LFS. Decorative is $7 or $8/lb. Buying from the LFS is better to start even though online is cheaper. Usually it is cured better locally (but not always). Your salt mix is going to be around $35 for a bucket. Not sure what kind of filter you have, but I'll assume that you don't have an installed overflow and it's a "hang on the back" filter. If it is one of those corner filters or a sponge I'd spring for a Fluval U3 or U4 pump. They're cheap and will get the job done. Oh - and if it is an under-gravel filter dump it. They're more trouble than they're worth in a SW setup. Also, you'll need power heads in the tank. You want to move around 8X the total gallons of water per hour. In this case, 8x45. Best is to buy two or three rather than one high volume one so that you can move the water in different directions. These cost anywhere from $40 - $80 depending on their capacity. Sand you've already looked at (good, cuz I forget what it costs). I have a deeper sand bed, but I wish I had gone with just 2 inches as I need to stir the substrate now and then because it's so deep. You'll need a protein skimmer - buy one 2nd hand if you can. Also go with the rule of buying one twice as powerful as you need. That'll be around $100 to $150. Not exactly sure because mine was used. Let's see...hydrometer - around $10, thermometer - another $10, test kit - around $25. Figure in another $100 for odds and ends. Also, if the light is just some generic light you'll want to eventually buy a high end power compact with additional actinic bulbs (maybe even some lunar LED's). Those can be pricey and can wait.
That's all I can think of off the top of my head. If you get enough live rock then you really only need to worry about mechanical filtration as the live rock will be your biological filtration.
A 45 gallon tank isn't that huge. Therefore your water chemistry mistakes will be felt more than in a larger tank. For example, if you dumped too much of a chemical into a 45 gallon tank the fish will notice it more than in a 90 gallon tank. Just things to think about.
I wouldn't count on the live sand to cycle with. I'd count more on the rock. Sand is good for taking care of the nitrate, but live rock is better for the ammonia/nitrite parts of the cycling. There are a lot of different ways to start your cycle - some go with fish, some with chemicals, some throw a piece of raw shrimp in there, other throw some food in there. Anything to get the ammonia to build up. Then your live rock takes over.
Cycling can take anywhere from a week to a month to two months. A lot of people would probably prefer that you didn't even add a fish for a year, and then someone else will post that you should wait for a year and a half just to top the first guy. Typically you should be ready in about a month for your first starter fish. I used chemicals to move mine along and added my fish a little early - around 2 weeks in. It took a little while to catch up but my water is just about perfect now.
Read the Saltwater Tanks for Dummies book to get yourself started. It's pretty good. And when posting, take what everyone says with a grain of salt. Most of them have had their tanks up for years and setting up a new tank is pretty simple. It's easy for a lot of people to get high on their soapbox when they're already set up. It's a lot different when you have the itch and want to get started.
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