Hello,
I'm able to create your program in PHP.
I have built multiple amazon api programs in PHP and should be able to complete yours quickly.
Getting 250,000 prices won't be an issue at all. The API allows you to make one request per second, and we can get the prices of 20 asins at a time. This accounts to being able to get the prices of 1.7 Million asins per day.
I would need to go over your requirements for the offer attributes, but I'm sure that getting this information won't be an issue.
I look forward to hearing back from you.