Here is a quick list of some of the most common and therefore least valuable pieces of old money:
$1 Silver Certificates (1928, 1934, 1935, & 1957)
The average silver certificate from 1935 or 1957 is worth $1.50. Uncirculated examples are worth about $4. Yes, star notes were issued but they are not much more valuable. Yes, there are also prefixes like 1935A-H, and 1957A and 1957B, none of those really matter. All of those notes were printed by the millions.
1928C, 1928D, and 1928E $1 silver certificate can be valuable in high grades or as star notes. 1928, 1928A, and 1928B notes are common even as star notes.
1934 $1 silver certificates sell for about $10 in average condition and $50 in perfect condition. Multiply those values by four to get the value of star notes.
$2 Red Seal Legal Tenders (1928, 1953, & 1963)
There is a myth that two dollar bills are rare. Sadly, that is not the case. 99% of red seal two dollar bills can be bought for around $4 each. Some star notes from the series of 1928 (A-G) have the chance to be rare.
$5 Red Seal Legal Tenders (1928, 1953, & 1963)
Red seal five dollar legal tender notes are also extremely common. These can be bought in bulk for around $6 a piece.
$5 Silver Certificates (1934 & 1953)
All regular issue serial number five dollar silver certificates from 1934 and 1953 are dirt common. Star notes are another story. 1953B $5 star notes are very rare. All 1934 $5 star notes have the chance to be rare.
$10 Silver Certificates (1934 & 1953)
Ten dollar silver certificates can look exotic, but they are actually very common. 1933 $10 silver certificates are the exception to the rule. Those are extremely rare.
Anything Printed After 1949
The type of bills we use today are known as Federal Reserve notes. These were first printed in 1914 and they are very common. 1950 marks the first year that these notes really lose any possibility of having a collector value.
