The others have already given you plenty of good advice, but here's a couple extra points that you might consider:
1. You'll want some heavy-duty filtration for predatory fish, so be sure to include this in your budget. Sponge filters and HOBs are reasonably cheap, but canisters can get expensive.
2. Be reminded that your tank will sit empty for at least a month before you can put fish in it, to establish the bacterial colonies facilitating the nitrate cycle. Don't be hasty, you will plenty of time to read up about various species and pick one that will suit you regarding appearance, required care, hardiness, predatory behavior etc.
3. If the fish you want is compatible with it, get some plants for your tank. They look better, and they're generally easier to maintain because the plants will metabolize nitrogen compounds (i.e. fish poop). Aggressive, fast-growing plants such as duckweed, guppy grass and pothos are especially useful, since fast growth means they will be "hungry" for nitrogen and deplete it quicker. Simply remove excess growth every other week and you'll be good to go.
4. Once established, tanks are relatively cheap to maintain. As mentioned, food for predators can be supplied from the supermarket, and even top-of-the-line fish food is not especially expensive. Water must be treated with a dechlorinator (at least if your tap water has chloramine instead of chlorine), but that is also relatively easy to budget. Most of your spending will be towards that initial purchase of the tank and its accessories (tank, stand, heater, filter, air pump, test kits, hoses and buckets etc.)
5. Check your tap water's parameters, especially its pH and hardness. You can probably find this online. It will inform what kind of fish will perform best in your tank, and let you narrow your picks.
6. Speaking of your picks, consider what you want from your tank. Do you want a unique, interesting-looking fish to act as a conversation starter? A pet that will follow you around and engage with you whenever you're in the room? An active predator that will jump out of the tank to take food from your hands? A relaxing, low-maintenance setup that will help you wind down after work or school? A breeding pair of fish to sell the fry and make some money on the side? If you have a better idea which direction you want to go, you can choose your fish with that goal in mind.
7. Understock your tank, at least at the start. Fish, even rare fish, are surprisingly cheap compared to the tanks required to house them. It's very easy to get excited over every new fish you see, and end up with a kitchen sink tank that is more fish than water and houses a dozen incompatible fish trying to kill each other.
Given what you've said so far, I think it would be ideal to start with a red wolf fish (as has been suggested), solitary piranha, mid-sized puffer, hujeta gar, single JD cichlid, or other solo-species project. This would be easy to maintain and serve as a good introduction to the hobby.