Hello Airbus Boy -
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A type rating can be as inexpensive as US$ 6,000 or go as high as US$ 20,000 in the USA, depending on type aircraft and requirements - In Europe, prices are substantially higher - as I see you are from UK. The less expensive ratings quoted at US$ 6,000 are for B-737 and DC-9. Takes 3 to 6 weeks.
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Pilots who "buy theirselves" a type rating are doing it to be more qualified and in hope to be selected for hire by an air carrier. It also happens that a potential airline employer will specifically require a certain type rating from applicants to be considered for hire.
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I have heard some companies telling applicants to get qualified with a type rating, and would be reimbursed, but honest, it is extremely rare. My airline requires a B-737 or MD-80 type rating to be considered for hire, this to select pilots who have showed their ability to succesfully complete training in a given type of aircraft.
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Do not believe that airlines do this, to get "trained pilots" and save on trainng costs. Even though we require, say, a B-737 type rating, you still have to complete our complete specific airline training as if you never were trained in that aircraft. In the past, there were too many trainees who failed in training. Nowadays, with the type rating required, almost every new hires complete our training succesfully.
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As to getting reimbursed by the airline for your type rating, may I smile and say, we do not do that... Or should we also reimburse your training costs for PPL, CPL/IR and ME...
If you do a type rating, I would suggest either the A-320 or the B-737.
I wish you good luck and all the best.
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Happy contrails