I also used to think £75 should buy a pretty good pair of bins and that 'budget' ones were more like £25. Apparently not.
If you read bin review sites and start looking at specialists, few better outlets stock anything much under £100. Budget would be defined as < £150, mid market £150- £350, and 'premium' £1000+. How the other half lives !
In terms of optical and overall quality, if one trusts the ratings given on a review site I found, it seems to buy a nice usable good budget pair with a 70% rating your looking at £100, to go to 'excellent' 80% will be around the £300 mark, and if you want that extra elusive few degrees of stunning clarity your restricted to makes like Swarovski which few of us can afford. The highest rated 97% Swarovski will set you back about £1500, or slightly less than I paid for my last 2nd hand Audi A4 car. You're paying for superb quality, but also a lot of money spent on glossy magazine advertising to build a brand of 'male jewellery'. Lower cost ones without the poser value that aren't international fashion statements (such as Vortex Razors @ £1000) might match the optical quality. It depends if you want to use them, or be seen wearing them.
I'm trying to justify spending £165 for 80% optical quality, I shan't be going down the polo club with them. I like the way the Vortex Diamondbacks will focus down to 4.5 feet, nice for watching the bees and flutterbies.
For anyone interested, this is the review site I've been perusing;
http://www.bestbinocularsreviews.com/