Hi,
You could try a River Reef, they do them in 48Litre or 94Litre sizes, I have just set one up and I am very pleased with it. It comes with a filtration system,and heater. You will need to add sand, live rock, and a skimmer (nano size,maybe a V2) and of course made up water (RO with added salt).

I did mine for £399.00 without any corals or fish, but pleased with the result,and for a first time venture into marines,not massively expensive.

Like you space is an issue for me,and money come to that. I opted for the larger 94Litre, but I have two 48Litres on the go for smaller freshwater fish and shrimp, and I am told these too can be used successfully,as smaller nano reef tanks.

Good luck,

Jon