I have lived in Herts/ Bucks and now Beds, for the last 20 years. Obviously property values are much higher the closer to London you are; for example I've just sold my one bed flat in Rickmansworth, Herts for £200k, whilst we've just bought a 4-bed, new build property in Bedfordshire for £245k.
-- Best locations for commuting to London from Herts include: Harpenden, Berkhamsted, Watford, St Albans, Rickmansworth (the first three are mainline train, the last one is on the tube).
-- Best locations for commuting to London from Bucks include: Chesham, Amersham, Great Missenden, Aylesbury (first two on the tube, last two mainline).
-- Best locations for commuting to London from Middx include: Northwood, Harrow, Pinner, Stanmore, Ruislip (all on the tube).
-- Best locations for commuting to London from Beds include: Milton Keynes, Luton, St Neots, Stevenage, Welwyn Garden City (mainline rail).
** Worth noting that because the Metropolitan and Jubilee lines are old they often have track problems.
To give you an approximation of time to London, travelling by tube from Northwood to Baker St is about 30 mins. Rickmansworth - Baker St is about 40 mins, Amersham about 50 mins. You should allow an extra 20 mins on top to get across town to the City/ Canary Wharf. By mainline rail, Watford is approx 40 mins away, St Albans and Berkhamsted about 45 mins, St Neots is 50 mins. All the mainline trains come into the City (Euston, Kings X, Moorgate).
You will find a property within your price range with relative ease and plenty of green space in BEDS, but you will sacrifice that for the commute. Good shopping in MK and Cambridge.
BUCKS is beautiful and rural with lots of pretty villages, with prices to match. Commuting by rail or tube will be expensive.
HERTS will be slightly more expensive, with leafy countryside and country pubs as well as decent travel links to the rest of the country, but depending on your preference you may find that you can compromise on space and keep your commute reasonable. Good shopping in Watford, St Albans and Brent Cross at a push.
MIDDX will probably be most expensive, because you are so close to London, but equally it will be more built up and not as pretty. Commute is usually good but crowded. Best shopping at Brent X or Westfield White City.
Schools and facilities-wise there's a massive range within each of the counties so you're best off drilling down once you've found the area you like best, but the pace of life reflects the style of living but generally, the further out you go the less stressed, and more relaxed it seems to be.
Hope this helps!