Wow, thanks for your great advice and all the info. Now that I have started back to work, my husband's family has been very supportive, especially my mother-in-law.
My milk did start to fail this week - I work until 10pm and by the time I get home my son is asleep, and he sleeps until 2:30 or 3:30. So I go about 12 hours without feeding him... I wouldn't have a problem if he woke up earlier, but he has put himself on that schedule, and I really see no reason to change it. He's been gaining weight terrifically, and he's very alert during the day, and takes naps like 'normal.'
So, my husband and I did decide to rent a hospital-grade pump, since 1) we want him to have breast milk as long he'll take it, and 2) it's actually cheaper to rent one or buy one just as good than to buy formula if I wean him.