Is it considered rude or odd

Hi - just checking with everyone before going to Japan -
Is it considered rude or inappropriate to reply (kindly) - "I'm sorry I cannot afford that" in a store or hotel (when offered a service)?
In Europe it varies from country to country.
Thank you for your input

People won't really say that they "cannot afford" it. I mean, it is not rude, but there is no need to state the reason. I would just say:
- Iie, kekkou desu. (No, I'm fine without it.)
- Iie, yamete okimasu. (No, I'll pass on it.)

A simple "no thank you" is polite enough, no need to go into your financial history. At best it would be inappropriate only in that you are giving way more information/explanation than necessary, at worst it could be interpreted as a passive-aggressive comment on their prices or services.

Thank you - really appreciate your comments.
I'll memorise those sentences - I realise I must try to be more reserved in Japan - but it's a bit difficult as it goes against ingrained behaviour - I'll have to be careful.