How much should I spend ?
It depends on how much time you envisage spending on your hobby. Remember you will be subjecting your (precious) eyes to long periods of magnified vision, focusing, re-focusing etc. The simple advice would be - go for the most expensive pair that you can afford and try to get a balanced view on your 'investment' by looking at the cost of other 'hobbies'.
Golf, for example could be classed as an expensive hobby, with expensive equipment and ongoing expenses such as course fees. A pair of quality binoculars might set you back say £1000, but they are likely to give 30 years of pleasure and outstanding performance. Put simply that's less than 10p a day !!
There are a rang of binoculars and scopes to choose from at the bottom of the page here.
The following information is aimed at giving you a basic understanding of how binoculars work, the different specifications available and what they mean, plus some points to help you make a more informed decision about which model to choose.
Where will I be birdwatching ?
Worth considering is 'where will I do the majority of my birdwatching ?' .For example, if your local patch happens to be a reservoir, lake, marsh or open moorland, or perhaps you live next to the sea, or an estuary ? then generally, it will be a struggle with a magnification of 7x or 8 x. It may be better all round to opt for 10x magnification, or even better, a telescope. Having said all that, many modern binoculars also will have 'close focusing' so a 10x model with close focus would also perform well in woodland or hedgerow. So the close focus option should be looked for in all magnifications. The very last thing you want is for a beautiful dragonfly to land three feet away or glimpse a migrant Firecrest and you are forced to walk away from it in order to focus your binoculars !
As unfortunately it will probably have gone by the time you're ready.
Look for 'minimum focusing distance' when choosing.