When accepting a favor would impose a financial burden, I usually push back twice and then relent. (1) "Are you sure, I can absolutely get this?" (2)"It's really not a problem, I don't mind paying." If they're still insisting at this point, I'll pack down, especially if it's obvious they're trying to do a nice thing.
I used to be more reluctant to accept that sort of help from folks, but there's a quote from the Thomas Covenant series that goes something like "in accepting the gift, one honors the giver." It's kinda stuck with me since I read it; let people give you gifts, it makes them feel good. Graciously accept, and think about how to pay it forward/back.
Couldn't agree more. I grew up poor, and I've been lucky to find a well-paying job in my adult life. It makes me feel so good to be able to do the things for people that I couldn't do when I was younger. I love that quote too - that's totally true for me. I think I get more satisfaction out of being able to offer something than the person actually receiving the thing.