Underestimating the journey to Labenne is all too easy and you need to study the route and plan the timings carefully. Visitors travelling by car from GB should allow a full day for the journey, even if travelling down one of the shorter motorway routes (starting in St Malo or Caen). If you start at the eurotunnel or Calais it’s probably worth considering a night stopover.
Travelling by car and ferry is probably the most popular choice and enables you to explore the whole region of France (and Spain) in your own car. From Britain, the shorter channel crossings (eg Dover to Calais) are less expensive than the westerly routes (eg Portsmouth to Le Havre/St Malo) but the journey is longer (and motorway tolls & fuel costs have to be added to the cost).
From UK the overnight ferry crossings might seem expensive but they work very well for SW France because the early start makes it relatively easy to reach your destination in a day (especially from St Malo = 7 hr drive + 2 hrs stops). Eurotunnel is very slick and will save you several hours on the channel crossing but this will be largely offset by the longer car journey which is effectively the same as starting from Calais.
The airport at Biarritz is served by the budget airlines: Ryanair (flying from Stansted) and Easyjet (Bristol and Gatwick) as well as Air France (Heathrow – changing in Paris). Cars can be hired at the airport (1/2 hour journey) but it is also possible to reach Labenne-Bourg by public transport (bus/train). You may have to walk the final 4km as there are only 2/3 buses/day serving Labenne de L’Ocean, or you could take a short taxi ride from the station.
Train. It is possible to use the channel tunnel and complete the whole journey by high speed train. The TGV stops either at Dax or Bayonne (1/2 hr by taxi). Or, if you insist on travelling the whole route by train, there are services from Dax and Bayonne to Labenne-Bourg which puts you within a short taxi ride (or 1/2 hr walk).