Intel's ark lists the 4690k as end of life. Expected discontinuance is 7/14/17. It's going on 3yrs old and it's technically 3 generations behind if you count broadwell. It's not uncommon for discontinued cpu's from intel to go up in price, it happens with all of them. A 4670k or 3570k is more expensive new than a 6600k or 7600k. When the 4690k was the newest cpu the 2500k's were more expensive new in box.
As others suggested your best bet is to find one used off ebay or similar. Using paypal and purchasing from someone with a fairly high transaction rate and positive feedback along with doa warranty (those who state they will replace/refund of product arrives dead in their ad) should be fairly safe. You might get lucky with a winning bid and pay less, some are selling used nearly for what they cost new back when they were available.
Still a cheaper alternative than buying a new motherboard, 6th or 7th gen i5 and ddr4 ram along with reinstalling windows all over again. Even if the price for the cpu seems a little expensive, overall the upgrade would still be significantly less with just a fraction of performance loss compared to a 6th/7th gen.