If you need to add one, a soundhole pickup would work and you could move it from guitar to guitar if needed. Fishman, Dean Markley and Seymour Duncan have them for 30-50 bucks.
I would suggest holding out for a used guitar that already has an under saddle pickup installed in...should be easy to find as it is the standard pickup installed for so many years for inexpensive guitars. Yamaha is good option.
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Paul
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