With your budget I would consider two paths, start out fish only and don't buy lighting yet, or just pick things up as you have money to.
I would highly recommend a sump for several reasons, the main being extra volume in a small system.
Also I would just like to say that if you are on a tight budget, start up cost is only the beginning. Things begin to add up as you factor in electricity bill going up, and buying new lights every half year(unless you save up for led.)
I would strongly suggest you save up more money unless you can find some killer deals on equipment. $400 would get you a tank, pump, power head, and skimmer. Then you need $50 in salt, $150 or so for ro/di. Test kits $20-$100. If you go with a sump add another $50. These are more like minimum costs in cost cases I'd say. And... We haven't even gotten to the expensive part, the stuff that goes in the tank. Sand and dry rock will easily be another $100 for a decent sized tank, and LR would be way more. Then we get to the fish which is extremely variable, but they can be had later on. If you are still considering coral add $200 + for good lighting and probably $100 in dosers and starting off with better equipment to meet the demand of them. Also the hidden cost in coral is addiction, I saw someone say on here that if you have a reef you need to factor in $100/month in frags/colonies. It was a joke but sadly true.
I do not mean to scare or discourage you, but merely want you to be aware of the real cost. A lot of people like to call BS when people throw out the $1,000 mark and yes, you don't even need to spend 1/4 of that on a tank/stand/sump if you get good deals but to do it right things add up quick.
With that said I still think you could pull off a smallish fish only system.
