Edit - 10k miles yearly ;)

I have a Citroen C1 (same as 107 and Aygo) and they get 50-60mpg (real world). I currently get around 55mpg with mixed driving. Cruising on on the motorway at 70mph you can expect just under 60mpg, stick to 60mph and it do a little over 60mpg. Performance is relatively good for these 1.0l engines. Acceleration isn't so good at 60+mph, but it's perfectly adequate in my opinion.

The 1.2 Fiat Panda is also another option, but probably not as efficient as the C1.

I just had a look to see what's available. You may struggle to find a good C1 for £3000. However, with the Panda you can get a well speced one for that price. I saw one with pretty much everything (air con etc.) for less than £3000.

Edited by P3t3r on 26/03/2014 at 12:08

My experience of a 107 (driven on Yorkshire hills) was getting 49 mpg. Driven the same way a 1.3 first generation Yaris got 46 mpg. I would suggest you look for a late first gen 1.3 Yaris, which is quicker than the 107/C1, more at home on the motorway, and uses only slightly more fuel, and from the sounds of it, quite a lot less than the current Polo. And although the reliability of the 107/C1/Aygo is very good, i think the Yaris is probably better still. Only real down side to the Yaris is its handling, its quite a pudding, and the 107s etc are a lot more fun. probably not an issue to your wife though.