I suggest using alternation group with capture groups inside to only match the numbers before or after your constant string values:
(?:Rs\.?|INR)\s*(\d+(?:[.,]\d+)*)|(\d+(?:[.,]\d+)*)\s*(?:Rs\.?|INR)
See the regex demo.
Pattern explanation:
(?:Rs\.?|INR)\s*(\d+(?:[.,]\d+)*) - Branch 1:
(?:Rs\.?|INR) - matches Rs, Rs., or INR...
\s* - followed with 0+ whitespaces
(\d+(?:[.,]\d+)*) - Group 1: one or more digits followed with 0+ sequences of a comma or a dot followed with 1+ digits
| - or
(\d+(?:[.,]\d+)*)\s*(?=Rs\.?|INR) - Branch 2:
(\d+(?:[.,]\d+)*) - Group 2 capturing the same number as in Branch 1
\s* - zero or more whitespaces
(?:Rs\.?|INR) - followed with Rs, Rs. or INR.
Sample code:
import re
p = re.compile(r'(?:Rs\.?|INR)\s*(\d+(?:[.,]\d+)*)|(\d+(?:[.,]\d+)*)\s*(?:Rs\.?|INR)')
s = "Rs. 2000 , Rs.3000 , Rs 40,000.00 ,50,000 INR 600.25 INR"
print([x if x else y for x,y in p.findall(s)])
See the IDEONE demo
Alternatively, if you can use PyPi regex module, you may leverage branch reset construct (?|...|...) where capture group IDs are reset within each branch:
>>> import regex as re
>>> rx = re.compile(r'(?|(?:Rs\.?|INR)\s*(\d+(?:[.,]\d+)*)|(\d+(?:[.,]\d+)*)\s*(?:Rs\.?|INR))')
>>> prices = [match.group(1) for match in rx.finditer(teststring)]
>>> print(prices)
['2000', '2000', '20,000.00', '20,000', '200.25']
You can access the capture group in each branch by ID=1 (see match.group(1)).