DDR4 is starting to arrive at NewEgg and some kits are actually in stock for those who want to be the first on their block to have these new DIMMs and can remortgage their home. The price of Haswell-E CPUs and motherboards is as of yet unknown but looking over the past few years of Intel's new processors you can assume the flagship processor will be around $999.99 with the feature rich motherboards starting around $200 and quickly raising from there.
At the 16GB mark you have more choices with Corsair joining in and a range of speeds that go up to DDR4-2800 as well as your choice of a pair of 8GB DIMMs or four 4GB DIMMs. Corsair was kind enough to list the timings, the DDR4-2666 @ 15-17-17-35 and the DDR4-2800 @ 16-18-18-36 though you will certainly pay a price for the RAM with the highest frequencies.
For those on a budget it would seem like waiting is your best choice, especially as Amazon is offering a limited selection of the new kits, as there is only a single 8GB kit from Crucial although you can buy two of the single DIMMs without heatspreaders for $110.
Intel product releases are always dearly priced, the introduction of a new generation of RAM is both exciting and daunting. You will see power reductions, base frequencies that were uncommon in DDR3 and very likely an increase in the ability to overclock these DIMMs but it is going to cost you. If Haswell-E is in your sights you should start planning on how to afford replacing your CPU, motherboard and RAM at the same time as this is no refresh this is a whole new product line.