Apologies if there is a thread with this already, I've had a quick search and not come up with anything!

So I have been thinking about buying a bike for years now. I am an avid cycling fan but never got around to owning a bike (unless you include the one I had as a kid).

The problem has been that it is such an expensive start up cost. However, now that I am running more than ever, I think it might be a good investment for commuting/cross training/longevity, etc and for years now I have wanted to try cyclo-cross racing. Considering that I probably have zero bike handling skills this is likely to be very funny/messy.

So, let's say I have saved my pennies and have around 500-600 to spend, what's the best way to start?

For a start, I don't know how reliable second hand bikes are. For example, would a second hand cyclocross bike be worn out/prone to mechanical problems and how likely is it that I am getting a bike that has been knicked? Are there any reliable online second hand retailers?

Secondly, how important is related kit? Obviously I need a helmet, pump, lock, spares etc. but are cycling specific shoes and pedals a must? Can I get away with running shorts rather than cycling specific shorts, do i NEED a cycling jersey/ water proofs if I already have ones for fell running?

Finally, a lot of things I have read go on and on about bike fit and most recommend going to a proper cycling shop for the first bike but most shops I look at seem to assume my budget is much (!) higher than it actually is. So how reliable are the basic height to frame size coversions?

Thanks for any help!

Matthew

PS. On the cycle to work scheme: as a PhD student I get some funding to tide me over but I am not eligable for the cycle to work scheme because I am technically not employed by the university.