All depends on the grade of the coin. Is the coin raw, slab, a proof, P mint, or a D mint? They will range from $7.00 to $450.00 in MS grade and higher in PF.
1964 JFK's are ususally just junk silver, unless a high grade. Melt is around 8 X face. Perhaps a bit higher.
Currently based on Silver price, the 1964 JFK has a silver value of about $4.70. My dealer (whose main business is as a jeweler) would probably pay about $3.75 a piece for them and would probably sell them to collectors for $5.00 a piece... Mostly he buys them up and sends them away to be melted.
I run across random '64 halves in antique shops. Sometimes they are way overpriced but I found one earlier this year at $3.50. Not a big deal but it pays to keep your eyes open wherever you go.
I used to buy them for $2.50-$3 each---since silver has gone up I haven't gotten anymore---but still get some in change every now and then....also get some 40%'s... Speedy
Unless certified, do not pay more than spot price currently around $4.50 to $5.00 even for uncirculated. There are so many of these about. I only pay premiums for Kennedys that have been certified, even if I agree with the sellers grading. If the seller won't sell for that, I move on. Delawarejones