Well, I'm not very good with knowing total costs of various size aquarium setups in my head (there may be others who are) but I'll throw in my 2 cents of comments since I always think its great when new members try to ask questions and plan ahead! Its wonderful to plan first of all for your hardware, even before (or simultaneous with) learning water chemistry and water change techniques etc. that should be learned prior to getting fish. If you have the patience you can learn a lot of things about the necessary hardware.
Unfortunately, its a very big topic and many hobbyists refine their opinions about the best equipment for their goals over a period of years and trial and error. Each topic, tanks, filters, heaters etc. can be searched down, using the forum search tool. There are long discussions of each topic and if you are patient, you can usually find a few long, thorough, discussions on each topic. There are opinions out there about the tanks themselves of course and certainly plenty of discussion about the various dimensions of the tanks (its great you are thinking about a larger size as these are usually better for more stable beginner experiences with water chemistry.) Tetras like neons/cardinals give you a very wide range of tank shapes that should work well.
Lighting will take on a lot of importance if you plan to grow live plants. Unless you have looked into the planted tank hobby and are interested in high light, high growth setups, you would probably want to go for a "low-light" approach and plan on about 1.2-1.5 watts/gallon of lighting. This very rough statement may be oversimplified but its just to get you thinking about the lighting in the hoods of the setups you will see.
The filter is by far the most important piece of equipment usually and is the subject of huge discussions in the hardware forum. For a beginner planning something near a 50 gallon, I'd recommend you probably take a step back from the highly technical sumps, and focus your attention on external cannister filters. There are, of course, various major types of filters. Expert aquarists can make almost any of these types work properly and may argue that they can do a fine job. For beginners however, I'd venture to make some generalizations. Undergravel filters are pretty much old technology. Internal filters work well but take up room inside the tank and usually have less media volume than you will need. External hang-on-back (HOB) types also have somewhat smaller media volume and can generate water noise returning the water to the tank. For these reasons, external cannisters gained a prominent position among hobbyists. They have greater media volume (very important, keeping in mind that mother nature provides near infinite "media volume" in natural habitats!) A general starting guideline to size a cannister to a tank is aim for what we call a "5x turnover rate (per hour)." Thus the aim would be 250 US gallons/hour flow flow rate (950 litres/hour) for a 50 US gallon tank. Starting around this tank size and above, many hobbyists opt for 2 cannister filters of lesser flow rate, so that filter cleanings can be alternated and filtration has redundant backup (all assuming you can make it happen in your budget, which is tough! Probably only a minority do this.) People get very religious about filters, so just be ready when you search the hardware forum!
Be aware that there are many things to learn about filters. The media (ceramic rings, ceramic pebbles, coarse sponges, fine sponges, floss etc.) are a big and important topic and most hobbyists on this forum (I would guess) modify their media choices, changing them from what the manufacturer recommends. Its important to explore this topic within the forum prior to starting your fishless cycle.
Heaters are an easier topic as there are many reliable choices. Heaters can be internal, but there are also external choices that splice into the filter tubes, thus keeping them out of your aquascape. There are sizing guidelines to be found within the forum and again, redundancy or having a spare can be an advantage.
Anyway, good luck and be sure to return back here to the "New to the Hobby" forum as your gear gets finalized and you are ready to start learning about the Nitrogen Cycle and Fishless Cycling, which are the first of the essential knowledge to go along with the good equipment.
~~waterdrop~~