As for cost, do you mean that the decline in prevailing interest rates requires setting more aside for a given annuity, e.g. pensions? It that where you get your estimations for worth (as distinct from cost)?
Management costs for DB pension plans have increased while management costs for market-based DC plans have plummeted (these price increases also track the rise of Vanguard and low-cost mutual funds).
Also, in that time period, a lot of major pension plans were financed based on calculations about market returns and interest rates that didn't bear out. But one of the defining attributes of a DB plan is that its payments are predictable to future pensioners, so all those financings had a ratchet effect.
Pension plans are currently not allowed under federal law to fully fund themselves because that would be so expensive it would disrupt federal taxation. Instead we are constantly building up future pension crises that will have to be paid in higher taxes and economic chaos later.