The meltdown sent interest rates soaring and availability shrinking, but rates are declining and lenders are more willing to make loans that top the limits for Freddie Mac, Fannie Mae and the FHA. Rates on jumbo mortgages — loans of more than $729,750 in counties with the highest-cost housing — shot up during the financial crisis as lenders and loan investors shunned anything tainted with even a whiff of higher risk. Rates on big mortgages were especially high relative to those on smaller loans. But in a boon for borrowers in California’s expensive housing markets, the jumbo-loan market is starting to return to normal.