indeed, the money you would spend in the taxi would probably more fun enjoying the fantastic tapas/pintxos and atmosphere in Pamplona. HOWEVER, beware this is the time for the local festival in Pamplona (famour bull running). The bull running has been cancelled this year, but finding accommodation might be an issue.
Fortunately, there are other possibilities, like aproaching SJPP from Hendaye via train and spending the night in San Sebastian, a delightful city by the sea with extraordinary food possibilities. On July 10th you have 4 trains from Hendaye to SJPP, for example. You could take the train to IRUN (border), then simply cross a bridge to France, it is a 600 meter walk, and there is always something special about border crossing on foot (the route that some many Spanish exiles took fleeing from Franco).
The trains from San Sebastian to Irun run at these times on July 10th, and you would also have the Euskotren services, or bus services, San Sebastian (AKA Donosti) is some 40 km to the border only.
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then, from hendaye to SJPP, you have these timetables.
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