Hi Fuzz,
The C30 / S40 / V50 / C70 are all built on the same platform used for the Mazda 3 and Ford Focus of the same years. Supposedly 60% of the parts overlap... steering, brakes, suspension, electrical components etc.
I've replaced our S40 lower control arms with Ford Focus parts at a much cheaper price, for example.
Engines and transmissions are not shared - but the 5 cylinder Volvo engine and AW-55 transmission (AW stands for Aisin Warner, owned by Toyota by the way...) can be bullet-proof but don't like neglect. We were given an AWD S40 because a cheap aftermarket waterpump leaked and seized the engine - there is no water level sensor so you just need to check under the bonnet every once in a while...and used engines are starting to become harder to find. Because I had engine parts left over from rebuilding that car, I bought a manual C30 for my son's first car and it's fantastic, however...when I did a timing belt service I found that the previous mechanic had broken the timing belt adjuster and the timing belt was running very slack...another excellent way to ruin the engine.
Brakes and suspension wear out quickly, but are easy to replace. They wear quickly because that's the way to get improved performance...suspension bushes and brake disks in the 1970s pretty much lasted for life, but didn't work very well.
The P1 Volvo platform also has some other quirks - the ignition switch can give problems and is a few hundred dollars to replace, engine mounts fail often and are a few hundred dollars each usually, and driveshafts need a rebuild every 200,000km or so. The coolant reservoir needs changing if yellowed to avoid splitting. These aren't unique to Volvo - any car of the same age is going to have "quirks", but Volvo parts aren't particularly cheap and mechanics like to charge to work on them. This is a car platform you really need someone to check out for you if you don't know what you're looking at.
Parts are cheaper if bought from overseas (FCP Euro in USA is my company of choice). Both our S40 and C30 are T5 (turbocharged) versions which I love for the extra power, but the 2.4 is the choice for greater simplicity and reliability. As a first car - if you're interested in working on it yourself, it's an easy car to completely ruin - there are plenty of Volvo-unique procedures which are easy to get wrong. If you're not interested in understanding the mechanics or doing at least basic maintenance yourself - save yourself a lot of grief and buy a Yaris or Corolla.
If you have basic mechanical understanding (and sympathy) and have the budget for proper maintenance, the P1 platform can be excellent value. Just be very careful - most of the really cheap ones (and many of the more expensive ones) for sale will have issues lurking which will cost an arm and a leg if you don't have a good cheap mechanic handy or are prepared to ask advice here and slowly work through issues yourself.
