I'm guessing on an older Volvo petrol,you are spending close to €100 a week on fuel alone,plus tax insurance servicing tyres etc of maybe the guts of another 2k a year.If you can do without the second car,and the train times suit,that's the way I'd go.
Ford Focus 1.4 Diesel will give you a good return for mileage also...
Need to weigh up the cost of the new car (or one since '08), & associated costs for running the car, e.g. tax, insurance, servicing, tyres, etc (plus a % for unknowns), versus the current cost of running the volvo...
Depending on the year / mileage on the existing car - you might not get much on a trade in... again, off set that with advertising, "showing" the car to potential buyers, will take time... Try some of the car sites on line (cgb.ie, autotrader etc) to see what your type car is selling for - will give you a good idea of how much to sell it at.
Car rentals may be cheap, but it's the "add ons" that cost the money ... scratch / dent / marks - and you'll be paying dearly for that (unless you pay for cover all insurance). If you using rental cars for a period of time, will that affect your own insurance if you do get rid of the existing car you have...