How old before looking elsewhere?

We have a limited budget for a lightweight single axle 3-berth caravan and there are some very low-priced 'vans on the market - but how far back is it safe to go before you get into unreliability?  Is anything older than 15 years old too risky to even consider?  We were thinking of a Bailey Pageant Moselle or Elddis equivalent.  Many thanks for any feedback.