If you don´t have (or don´t want) to use Iberico ham, you can use serrano ham instead. Iberico is the best and will give an amazing and personal flavour to the tapa, but it´s expensive, I know. My recommendation, if you opt for serrano, try to buy a good one. The price is not the same as Iberico, much more affordable, but at least a quality serrano ham will give a good flavour too. Also, try some Iberico ham "de cebo" 50%, it´s more affordable and the taste is almost like the Iberico "bellota" 100%.