How to extract offer details out of an offer text?

Question

I want to extract offer details from the raw offer text. These offers could give cashback or discount or both. Some examples:

1. Flat 60% off
2. Get 10% off on a minimum purchase of Rs 400
3. Get 20% cashback of up to Rs 50
4. Flat Rs 100 off on a minimum purchase of Rs 1000
5. Flat 25% + Rs 150 off coupon code

I'm looking for a parser that returns the details from such raw text. These constructs are discount amount/percent, cashback amount/percent, minimum transaction amount, maximum discount/cashback, etc. One important consideration to keep here is that these offer constructs are limited. Should I go for a rule-based engine or NLP or something else altogether? What is my best bet and what should the output dictionary look like?