Split out your data in your repeating fields to separate related records. It will be much easier this way.
Although the suggestion by mr_vodka is correct (Thank you!), let's assume you remain fixed on using a repeating field.
Create a calculation field, "NumberCalc", that is also repeating. The formula would be:
Let ( x = Mod ( <Number field> ) ; If ( x ≥ 700 and x < 800 ; x ; "" ) )
Now, you can search this calculation field for an entry in this calculation field, and it will only display those values from 700-799
You can take this one step further by having another calculation "NumberCount" that counts the number of occurrences where 700-799 occurs. The calculation formula would be:
Count ( NumberCalc )
You can then perform a search on this field for a value greater than 0, and it will display all records that have 700-799 as the last three digits.
If you need clarification for any of the above steps, please let me know.