You don't need 6 meals a day, but if eating that frequently is the only way to get in the calories, then so be it.
If you can't leave your desk, I'd be pounding shakes (protein + oats + peanut butter + macadamian nut oil/walnut oil), greek yogurt, milk, tuna, nuts, nut butters, etc.
If you're broke, stick to cheap meats (chicken-whole, legs, breasts, etc., tuna, ground beef, and similar), eggs, peanut butter, oats, rice, potatoes, and veggies. Protein powder if you can afford it/need it. Milk to fill in the gaps.