The higher mag will demand a lot more from the glass. So your budget would get a much better 3-12x56, for example, than it will a 5-25x56.
Also- at the sort of mags you're requesting- scopes will be mostly target scopes. Big heavy beefy things with huge turrets etc. Are you happy with a monster on top of your gun ?
Also whats the lowest mag you find yourself shooting ? IMO you will use 3x mag wayyyyy more than 25x- even if its just to spot and scan for your quarry. But if a deer comes in to you at 25 yards......
You will also v likely shoot on a lower mag. You may crank it up to look at the deer better- but will often find yourself cranking it back down again after. Potentially shooting on 15x or so. Shooting a deer off sticks at 30x- you will be wobbling a fair bit- and it's v distracting, and noticeable- at 30x. Take the mag down to 15x- and you appear to be much more stable. Downbto 5x- and you feel rock solid.....
You could try and buy a cheap scope- perhaps a used £350 hawke (say it was £500 new) and just try it. If you love the high mag- but want better quality optics at that mag- at least you know what you need.
You may find 15x is more than enough, however...... That swaro linked above looks v nice. A delta titanium HD would do a good job. The 2.5-15 or 4-24 as someone has said.
If you really want to go down the monster target gun route- a secondhand Delta Javelin or Vortex would do.
Or a Bushnell Elite 6500 4.5-30x50 won't cost much as a trial scope.
You don't say what time of the day you shoot- but unless it's beautifully bright daylight- almost any scope at 25-30x will struggle for light and you will prefer the picture at lower mag......
Either way- you will end up shooting at 10-15x most of the time IMO. But try a few and enjoy the experiment