baby,
u would need AT LEAST a manual pump to stand by at home. cos like singapoh said, in the initial weeks u'll need the pump to help stimulate and increase yr milk flow. also, u won't know until bb is born if yr bb will hv any probs latching. if yr bb has probs latching like my girl did, then u will hv to rely on 100% pumping if u still want to bf and u'll need a good pump.
if u're really concerned abt the cost, maybe u can borrow from friends first then buy later after delivery.
also, wat is yr plan after 4 mths maternity? do u plan to continue bf or stop? if u plan to continue then u'll need a breast pump to pump during the day while u're at work. so may be a good idea to invest in a good one now?