olympic bar with plenty of weight.olympic zig zag bar(for tricep work and underhand rows). good quality stable adjustable bench. i have a power rack which allows the bar to be held for all barbell chest work and also any type of front or back squats, it also has a bar in the middle for chins, so this piece is extremely beneficial. the power rack can also be used to hold the bar for doing stiff leg deadlifts off a bench. make a block out of wood for calf work. a vertical leg press(cheaper than 45 degree) allows for training legs and calves(heavier than on a block).
i would say this stuff is bare essential for a decent home gym, followed then by dumbells, then maybe a lat pulldown machine for back and tries. seated calf machines are fairly inexpensive.
whatever you do, try and get as much as possible used, hell, if you need to spend $5 on a can of rustoleum to make it look better than do that.