Steinberg’s own Halion Symphonic Orchestra is one of the cheapest orchestral libraries around, but there are no choirs. You can use it inside Halion Sonic SE.
You can also try the demo for the full version of Halion Sonic 3 (included with the Halion 6 demo). They recently added several new strings, brass and choir sounds. The rest of the sound library is different from what’s included with Cubase, and it should be very useful for someone looking for cheap good sounds.
Yes it’s a generation old sampler and no longer is as good as contemporary Halion or Kontact, but for pop stuff it’s perfectly good, there’s actually a decent selection of strings, the choirs won’t blow you away but they’ll do the job. Some of the sounds are still pretty impressive and it’s light on system resources.
garritan has some decent strings/orchestra and choirs for very few bucks.
It’s not Vienna but it gets in the neighbourhood of what the real things do and the samples are a bit different then most. There are some very interesting patches.
Steinbergs symphonic orchestra is not 300 pound but rather 99 i would think, and if you wait out some weeks there will be the annual half price promotion and then it’s only 50 pound. By far the best option.