Sending my library to Manchester---best way?

Hiya--
Well, I'm leaving almost everything behind except a few clothes and  .....lots of books. Probably, nearly 800 books, but I'm not sure. 
What's the best way to send them from San Diego to Manchester?  I spoke with the post office today, and they told me it would be almost 150$ to send 40lbs of books! 
What are better options? Are there better options?
Should I contact a moving company? Or just start selling off everything else I own to pay for the book shipping?
Thanks!

Although it is nowhere as cheap as it used to be, you can send your books with USPS using M-Bags.  I don't think the person at the post office considered this option when they quoted you.  You can send up to 66lbs of books per bag at a rate of $2.85 per lb.
The rate they quoted you was closer to $3.75 per lb. 

Having no idea how much 800 books weigh (I'd wager quite a lot), this is probably not your best option.  Therefore, you could try doing a search on this forum for a company called UpakWeShip.  They're relatively cheap compared to other shipping companies.  I got a quote from them (this is from Philly, so don't know if it'll be more from San Diego) and I was quoted $900 for 100 cubic feet.  I checked on their website and to give you a rough idea of how large a 100 cubic foot space is, measure a square on your floor that is 4 foot x 4 foot.  If this space were to be stacked 6 foot high with boxes, then the stack would equal 100 cubic feet (4 foot x 4 foot x 6 foot). 

That price quote from Upak, bearing in mind that it's for a shipment from the East coast, would be for dropping your boxes off at their nearest warehouse to your residence, then having the shipment delivered to your door in England.

I also had a large library of books.  Everyone here talked about M-bags, but it ended up being way too expensive for me with the amount of books I had.  I ended up going with U Pak We Ship  http://www.upakweship.com/ and was able to send all of my books and other stuff for much less.  Since you live in a port town in CA, you will also be able to get a much cheaper rate than I did out of Idaho.   Give them a ring.  They are incredibly helpful and will reply promptly.  Alison was great (the lady who arranges things). 

I've contacted upakweship.  I hope it's reasonable... I just called USPS as well--and the guy on the phone told me that they don't do M-bags anymore! when I mentioned that they were still on the website he said "well, that doesn't matter--we just don't do them.  You have to send it priority mail."
Arghh.  I emailed them also, just in case this guy didn't know what he was talking about.

So, any other ideas?  Especially now that USPS is out apparently?

You could try contacting UPS about their freight service.  This is not the usual UPS service, mind you.  They have a leaflet in their stores talking about an ocean freight service for moving household goods that takes 6-8 weeks to arrive in your home in the UK.  The leaflet tells you to talk to your local UPS Store for more details.  Well my local UPS store has absolutely no information about the ocean freight service, and in fact, didn't know they even offered it - which I found odd considering there was a stack of leaflets right there on the counter that said "ask us about our ocean freight shipping service for moving households overseas." 
The manager said he would try to get more information for me, but that was ages ago and I haven't heard anything.  I'm not going to chase them down for info.  I'm inclined to think upak will be cheaper anyway.  But give UPS a try.  You might have more luck on your end.

I just thought of something else you could try, http://www.uship.com/.  Basically, you advertise your shipping needs: Need to ship 800 books from San Diego to Manchester.  And shipping companies will bid for your business.  It's sort of like eBay where the shippers have feedback ratings so you can choose a reputable company.