Steve, there has been some discussion in this forum about crawlspace recently. First, see "crawlspace projects" on Oct 15th, then the continuation on Oct 18th. Generally, you would use an R40 for a 2X10 joist. This is most common in ceiling applications, but may a bit of overkill for your kitchen floor. I would look into a couple layers of R12. R12 is generally the least expensive, as it is the most used in construction. With two layers of it, and an air space between (not manditory), you would probably achieve the results you desire. You don't necessarily need to put plastic on the ground, but a vapour barrier stapled to the underside of the joists would be a good idea once the insulation is in. The vents, I would close off in the winter.