Are you open to modifying the new car?
You could pick up a decent vag 140 diesel for say £3 - 3.5k, then spend the rest at somewhere like darkside developments on an uprated turbo kit, clutch/dmf, etc. The 140bhp diesel engine will easily handle 230bhp and the torque increase once the clutch and dmf has been sorted.
I moved from a 182, to a 2.0tdi jetta (140) that i paid £3k for. The turbo failed after a couple of months so I opted for a hybrid turbo, because I wanted something stronger than the original turbo, but also more power as i'd also planned on remapping the car anyway. I'd have preferred to go to darkside developments, but they had a 3 month waiting list to get in and i needed my car.
The Hybrid turbo was £1000 fitted and mapped, i'm still on the original clutch and dmf, and i've covered about 15k miles now. Power is a little over 200bhp, and compared to my 182, it's probably <1.0 second slower to 60, but it's probably a little quicker if anything from say 30-40 onwards. It's definately not as fun to drive though, but i've recently upgraded the dampers and springs to help that a little.
I expect the clutch and dmf will need replacing at some point, but they surprising still going strong and showing no signs of wear.
As for mpg, it currently cost me around £52-54 to fill the tank (always refill to full once the light comes on), and i'll get at least 550 miles from that, best yet is 655 miles over a week of use, but that included a couple of site visited that i took it steady on over probably around 300 miles. And my commute to work is quite economical.
Just another option and the way i ended up going from my cliosport. It wasn't all intentional and i originally moved from the clio to the VW to save money and move away from modifing my car. After just over a year of use i've probably not yet broken even on the extra cost of the turbo over the savings i've made in fuel, and a clutch and dmf will probably take almost a year to break even on once they need doing. But i needed a bigger more comfortable car for my growing family, so need to move on sooner rather than later anyway.
Plus i'd have probably spent quite a bit of money on the clio if i'd have kept it longer. Still miss that car, and find myself looking at the classified section on the cliosport forum.