I disagree, speaking as someone who's keeping a 2007 iMac running on the latest software just for giggles has has upgraded several Macbook Pros.
You can put 8GB of RAM in a 2009 Macbook Pro (it probably currently has 2GB). Crucial part CT3309351, £45. 8GB is more than enough: it's the maximum available on Airs and the new Macbook, and I'm running several machines on Yosemite.latest with 4GB with no signs of distress.
You can put a 500GB solid state disk in it. Samsung 850 EVO, £129. That's probably a lot more space than you currently have.
Total £175, and it'll perform as well as a new machine for anything other than highly CPU intensive jobs.
£25 for someone to do the work if you don't fancy it. But RAM and hard drives on 2009 Macbook Pros are the work of five minutes each.
Apple will do the battery, fixed cost, for a further £99 I believe.
So less than £300 for an effectively new machine.
If you need more disk space than that, you can do trickier things involving replacing the hard drive with an SSD, the DVD drive with a hard drive, and building your own Fusion drive. Then you can put 1.1TB into your Macbook for about a total cost of £100 (£50 for a 128GB SSD, £40 for a 1TB hard drive, £10 for the bracket). That's what I've done on my iMac. But that's outside the realm of simple upgrades, and your local "I take macs to pieces and put them back together" man might not know what to do. If you fancy it: www.royr.net/2012/11/how-i-installed-2012-fusion-drive-in-my.html