I use the Medela mini too MoosMa. I was given mine as a present, but it cost about £42 new from a shop on ebay. I have found some bottles that plug into it, but not used avent ones so I can't be sure about those. I've got closer to nature bottles, which definately don't fit. I find it very handy to use with the batteries, so I can express wherever I am, or even as I wander about.
I did use a medela symphony in hospital, a very big fancy bit of kit, no idea what they cost, but suspect it's a lot. The main advantage of that was having two cups, so it took half the time, although it really did make me feel that I was hooked up to a milking machine.
I believe you can also get expressing bras, where the pump is hooked in and held in place leaving your hands free. Not elegant, but leaves you less tied up if you are expressing a lot.
Also, when Sandy and I got home from the hospital our bfing had got to the stage where he was on EBM and formula top ups all by bottle, and I thought that was going to be it for good. But just a couple of weeks later he is now largely back to being bfed directly, so it can still be possible to go back to the breast later if you want to.