well, this is complicated, and im so sorry you have to go back to work. remember that full time nursing is possibly and protected so pumping is a great option. i know my insurance covered the cost of a pump as long as my dr prescribed it, and i got the medela pump in style! :D FREE.
so check on that.
however, with your baby, you will just have to give it some time. i know you are worried if he doesnt eat anything, and thats normal and natural, but KNOW that your baby will NOT starve himself. normal healthy babies will eat when they are hungry. it might take some time, and 'strikes' are common, but he will not starve to death. give it some time, make sure that the person giving the bottle is not you (baby knows its you and will naturally prefer the 'real thing' LOL) and even leave the room, though it may be hard to do. he will use the bottle.
i highly discourage using formula as its not as good for baby - its harder on digestion because its more concentrated. its OK if you WANT to, its not that much worse nutritionally, but remember to add a little bit of water to baby's diet in order to try to prevent constipation, thats all. :D
anyway, good luck, just keep trying, and nurse/pump as much as you can. you can always store up lots of extra between now and when you go back to work, so that you possibly wont have to pump at work, or you wont have to pump as much. night nursing is GREAT and healthy and normal and natural for baby too so i hope you can somehow be willing to night nurse/cosleep for more of that connection when you are there. its not for everyone, but i found it very comforting and helpful to cosleep. my son coslept until he was between 15-17 months, he nursed and we both went back to sleep. it was awesome. :D
anyway, trust your intuition, and your instincts, about what to do. i know financial issues are a priority with everyone these days, but see if there is any way to alter your work schedule to work for your family. im sure you have done the math, and that day care isnt enough of a cost to validate you working or whatever.... you dont want to be spending more on day care than you viably make working, you know? i work at home, in home day care, so i not only dont have to day care my own child, but my child gets lots of in home companions/social life :D we love it.
good luck!