Hi and Welcome
The research I've done seems to indicate that the 159 is about comparable to its competitors in terms of reliability and MOT pass rates. There are some known issues with ensuring that the timing belt/water pump is replaced and oil changes are done on a much earlier schedule than the original manufacturer's specification. However, if you spend some time looking around you should be able to get a decent example within your budget.
I was able to get a well-presented version on an 08 plate with less than 45k on the clock for c. £7k, but I then needed to replace the timing belt/water pump, and some other bits, so I may have paid over the odds. As I got this work done at an independent alfa specialist, I took the opportunity to get a remap, so my total cost for the car (with this additional work) was in the region of £9k. I'd kind of factored the extra into my budget (which was the same as yours) so I was ok with this.
The car is beautiful and, after all the work, drives and handles very nicely indeed! So long as I keep up with the service schedule and keep it well maintained (and use a good specialist) then this car should last me for years. The mapped 2.4 engine is a delight so long as you are not expecting 50+mpg
. But as another contributor to the Forum posted, you don't buy an Alfa to look at the fuel gauge!
I still can't help looking back and smiling at it every time I get out of the car, and it looks so smart and distinctive parked in among the generic bmws, audis and volvos parked on my street.
If you can get a good example, lowish mileage and make sure its been properly looked after with timing belt/eater pump changed at under 40k miles, and regular oil changes (recommended c. 10-12k miles I think), that has been maintained and serviced by someone that knows what you are doing, you're on to a winner. Good luck!