Recommended intro tank for a low budget.

[JoJosReef]

@trevorhiller had some nice detailed info for you.

I think that the rocks/sand is the best place to bust your budget. Ocean rocks and sand just can't be beat, even if it costs you 25% of your budget. No need for bottled bacteria, less likely to get dinos or cyano and start dumping chemicals in your tank, less likely to get overrun by Green Hair Algae and spend every day plucking tufts out of your tank and then dumping chemicals in your tank after you've had enough. Mixing live rock in with the dry rock will definitely help, but that dry rock is just an open canvas for nuisance algae to take over...

Best thing I ever did in my second tank was go 100% gulf rocks and sand. Zero doubts. Even after my wife said "You bought a plane ticket for ROCKS!?"

For budget lights you might look at Noopsyches, which are all the rave right now (especially the K7 mini for nano tanks like the IM 15gallon).

 

[Lunatic Fringe]

I started with a 10 gallon Aqueon tank, Kessil A80 tuna Blue, 50 watt heater, AC-70 HOB Filter, a little rock and sand for about 300 bucks and had a pretty banging tank in a few months. It later became a QT tank minus the rock and sand, something I would highly recommend you have as well if this is a hobby you want to take to the next step. A ounce of prevention is worth a pound of cure as when you go to a bigger tank your going to have a lot of money invested in your tank and live stock! You'll be limited on fish going this route but you can do a lot of softies and LPS corals and cut your teeth before going all in on a larger more expensive set up. Water Quality can change quickly on you with a tank this small, but most issues can be solved with vigilance and weekly water changes. You'll will need to spend more on things like a test kit, salt, ect...but this will let you cut your teeth before you go bigger on your tank and keep more demanding things if you so choose. This aint the cheapest Hobby to get into, but sometimes a lack of funds is a blessing in disguise as it forces you to go slow!

There are a lot of good options out there depending on how long your arms are and how deep your pockets are. This is basically (Lighting technology wasnt what it is today back then) how I got into the hobby and worked well for me.