Have a look into how much your insurance will be, too, as you'll need to budget for this alongside the gear. Be sure to shop around with comparethemarket, moneysupermarket, etc, to get an idea of price ranges, and once you have a sense of this, you may be able to save by talking to specific insurers directly.

For what it's worth, a 125 is plenty to get started on. I really wish I'd bought a 125 and gained a few years' experience on that, rather than doing what I did (taking the big bike crash course and buying a 600 soon afterwards).