What Instrument Should I Get?

Bb Clarinet
If you want to start out on a regular Bb clarinet to get a feel for it, then the best (and cheapest) one that I have found is:

Buffet B12

Approx. Prices:
500 US Dollars
250 GB Pounds
450 Euros
(although cheaper online or second hand)

Made from ABS resin.
Standard student instrument.
Popular in schools.

Bass Clarinet (beginners)
The best bass clarinet to start out on is:

Yamaha YCL-221 II Bass Clarinet

Approx. Prices:

1800 US Dollars
1700 GB Pounds
2100 Euros

Also made from ABS resin rather than wood.
Low Eb.
Similar to the Jupiter JCL-675N Bass Clarinet which is a little bit cheaper.

Bass Clarinet (professional)
The greatest and most expensive coveted bass clarinet available is:

Selmer Privilege 25P

Approx. Prices:
14,000 US Dollars
7,000 GB Pounds
9,000 Euros

Made from grenadilla wood.
Low C.
A beautiful instrument.

A Word of Caution
Don't buy a dirt cheap no-name instrument: the keys will bend and it will sound out of tune!
Buy a Buffet, Selmer or Yamaha.
Buy from a reputable supplier.