It's hard to predict in advance what you will need and why. I fully intended to breastfeed, but then was faced with a baby who just would not latch, so I started pumping while still in hospital using hospital equipment.
Some hospitals will rent out pumps if need be (unfortunately not mine) so we ended up panic buying a Philips Avent before I could be discharged, which worked ok but died very suddenly after 6 weeks of heavy use (I was pumping exclusively,, probably for about 6 hours a day as it was a single pump). I had plenty of milk, and a very hungry baby!
I'm pregnant again, and this time around, I am looking into renting hospital grade double pumps from express yourself mums (other places exist). You can get one for £45 for 2 weeks, then £45 a month thereafter. If I need to do this exclusively, I want a really good pump so I'm not constantly attached to it (I'll have a toddler to look after too).
If you're just looking to pump occasionally to have a 'going out stash' then most single electric pumps will do. It's when it takes over your whole life it becomes very vital to get a good one like a Medula, and those aren't cheap!
Of course I'm rather hoping this baby just knows how to latch and I can return my pump after a fortnight. Fingers-crossed we all have an easy time of it!