I had this problem with DD - she still didn't quite have the hang of the bottle when I went back to work. She was 3 months old.
For about six weeks, I would go to her daycare every day at lunch to nurse her. Could you do that? At least then your baby would get one feeding during the day to tide him over. Or, can you go to work part-time? Drop baby off at daycare, and pick him up after 4 hours or so?
With our daughter, she would only eat from the bottle if she was calm... we could not starve her into taking it. Some things that we tried were:
- I nursed her for 5 minutes first so that she wasn't starving
- We would wait until she was calm in her bouncy seat, then sneak up behind her and put the bottle in her mouth
- Walk, rock, and sing... walk, rock, and sing... get her very calm and then rest the bottle nipple on the side of her mouth and let her decide if she wanted to take it.
I know you said you've tried all kinds of bottles... have you tried Dr. Brown's? We found that other bottles either flowed too fast or too slow, but the Dr. Brown's nipples were perfect for DD. That is still the only kind she can latch on to. She will also latch onto a breastbottle, but as you say, they're expensive. It may be worth ordering one just to see. The Avent bottles are supposed to be breast-shaped, but DD can't latch onto them. She hates them. She can only latch onto the normal "bell shaped" nipples like the Dr. Brown's.
If they keep trying at daycare to feed him bottles, he'll have rough days but he will eventually learn to take them. It took us like 6 weeks at home and then another 6 weeks at daycare, but then DD was a champ at the bottle and she still nurses with no problem too. Be patient and good luck to you....