This is a question I’m often asked. The answer is, it depends...
It depends on what your skill level is, what sort of riding you want to do, how often you’re going to use it, whether it’s for leisure or competition, etc, etc.
When you’re starting out, you don’t need to own a bike. If, for example, you want to wander up and down the River Exe cycle path: Route 2 Bikes in Topsham or Saddles and Paddles in Exeter (and probably other places along the way) will rent you a bike. If you want to try mountain biking, then Forest Cycle Hire up at Haldon is the place to go to to rent a bike. This gives you an opportunity to find out whether you enjoy cycling before committing to buying a bike. This worked well for two of my clients on my Get Back on a Bike rides who rented first, then bought their bikes second hand from Forest Cycles (c. £300 for a bike that would be £500 new). This way they knew they were getting a bike that fits them and is comfortable to ride.
You can spend vast sums of money on a bike. A quick search turned up an ad for the new Scott Genius 900 Ultimate Mountain Bike 2019 which retails for a whopping £9,499. At that price, I’d be scared to take it out of the house, let alone throw it around on rocky tracks!
But you don’t have to spend thousands. You can buy second hand - either online on eBay, Gumtree or PinkBike, or through the charities and social enterprises that refurbish old bikes, such as Ride On on the Quay, or Julian House Bike Workshop by the Corn Exchange, both in Exeter. The danger with buying online is that you won’t know whether the bike will fit you. It’s really important to have the right geometry, so you’re not too stretched out or cramped up.
The more you pay, generally the lighter the bike gets, and the better the components on it. All the bike magazines have reviews of bikes, which can be helpful and are often published on their websites as well as in the magazine. Essentially, the more technical the riding you want to do it, the more it’s worth spending on a bike.
If you’re just pootling around on green trails or converted railway lines, you don’t need suspension or bells and whistles. It would be more fun to have them, but is not essential. If going to the Alps for your holidays, and you’re riding up as well as down, then a light bike with good front and rear suspension will make life a lot easier.
So the answer to the question is no, you don’t have to spend a lot of money on a bike, but you may want to!