The value of any numismatic collectible is set, essentially, by supply and demand. "Supply" is more often referred to as "rarity," and demand ... well, is demand. :) Condition plays a part in demand, but sets in original Mint packaging are usually insulated from condition-based pricing variations.
The U.S. Mint does not make "proof mint sets" of any year. The two types of sets have very different coins in them. A 1980 PROOF set has a current value of $5.00 and was issued for $10.00. A MINT set has a value of $8.00 and was issued for $9.00.
No US proof sets were produced in 65, 66 or 67. Special Mint Sets were issued with coins that have proof like qualities. Issue price was $4.00 current value is $11.00.
NO US proof sets were made in 1965-1967 but they did make Special Mint Sets the coins in these sets do have some proof like details. Current retail value for a 1965 set is $8.00 issue price was $4.00
The 10-piece 2003 proof sets have a current market value of $10.00. Issue price was $19.95.
Proof sets were not made in 1965, but a 1965 special mint set is worth $12.00 USD.
The U.S. did not produce any proof coins in 1965, 66 or 67. The Mint issued Special Mint Sets (SMS) instead of proof sets. Current value of a 1965 SMS is $11.00 retail.
To begin with, there are Mint sets and Proof sets, and they're 2 different things. You'll need to check your set to determine which kind you have. Mint sets are sets of uncirculated coins selected from normal strikes. These retail for about $15 to $20. Proof sets are specially-struck coins that have mirrorlike surfaces and matte-finish images. 1995 proof sets sell at a fairly decent premium - cupronickel sets retail for $35 to $45, and silver sets are in the $80 to $90 range.
There are mint sets and there are proof sets, and they're not the same. Mint sets are ordinary-strike coins, selected for quality, and packaged at the mint so they're uncirculated and untarnished. Proof coins are specially struck on prepared blanks that give them a mirrorlike surface. They're minted separately from ordinary strikes and are intended only for proof sets. Please post a new question identifying which type of set you have so it can be valued. Thanks!
1936 is the year the mint started producing proof sets annually for public sale
There is no record of the Royal Mint having produced a "gold" Proof set in 1974, only the usual Proof set. Royal Mint gold Proof sets issued from 1980 contain only the "Sovereign" coinage.
Depending on what condition it is in, most proof sets sell for around $55.00. Some I have seen sell for $28.00 in mint condition. I own all proof sets from 1999-2009 and i can sell them all for around $609.00.
The U.S. Mint did not produce any proof coins in 1949. Mint Sets (uncirculated coins) were issued in 1949. The sets have two of each coin issued for circulation and were packaged in cardboard. Current value of a 1949 Mint Set is $1,000.00 to $1,400.00 depending in the condition of the coins.