When you say tight budget, are we talking under $300 total or do you have a bit more wiggle room? I'd actually push back on the idea that the chair has to be your biggest investment - yeah, lumbar support matters, but a cheap desk that's the wrong height can wreck your posture just as bad. If your apartment's small, consider a wall-mounted fold-down desk or even a sturdy table from a thrift store (way cheaper than retail furniture) paired with a basic ergonomic chair in the $100-150 range, or hunt for used office chairs that aren't necessarily name brands but have adjustable height and back support. For lighting, a decent LED desk lamp runs maybe $20-30 and makes a huge difference without eating into your budget - natural light from a window helps too if you can position your setup near one.