IMO, the tank look fine for where you are at in the tanks maturity. The light is probably not the issue. SPS tend to get better color as they grow into colonies. Although I hate those Chinese black box fixtures, I feel that you are not going to see much better results using a different lighting. The biggest issue I see with your SPS is you are keeping a leather coral. The leather and other soft corals of that type give off toxins that can irritate SPS. I have seen a lot of SPS tanks and all those with leather corals never achieved much more than decent colors. All those that had mind blowing colors were free from soft corals other that zoas and palys.
Change to Metal Halide in a tank that size, you will most likely have to deal with heat issues as well. Unless you have a large sump. Also you will have a tremendous amount of spill-over light as MH reflectors are designed to optimally cover tanks much wider than 18".
T5 is an option too. you would need to research what fits in your price range but you can't go wrong with ATI. You can find them right around your price range. However after adding bulbs you will be over budget.
http://www.marinedepot.com/ATI_36_I..._Light_Fixtures-ATI-UZ3307-FILTFIT56U-vi.html
As for LED, what you have is fine but you could look at the 27" Maxspect Razor as it should have enough to light that tank and be in your price range. It includes a simple 2 channel controller. I have a friend with them over his SPS reef and is very pleased with the results.
http://www.marinedepot.com/Maxspect..._LED_Lighting-Maxspect-0M30047-FILTHO-vi.html