If you don't already have one, get a yearly price reference, Spink's Coins of England or Collector's Coins (at the top of this page in the advert) will do and it doesn't have to be the latest volume either because all the types available are laid out and rarity pretty much correlates to price. Do the exercise and you will learn as you familiarise yourself with the prices, what constitutes an affordable year. or indeed whether it is possible.