Firstly, two threads you will find useful:-

LNF Successes

and

LNF Help Requests

With regard to your rejection based on "currency fluctuations", are the rates quoted elsewhere inclusive of tax? The rate on Marriott.com for most UK hotels is quoted inclusive of tax so that may be a reason. If you really are comparing apples with apples then a difference of over $30 really cannot be attributed to currency fluctuations.

Feel free to PM me with your dates and I'll have a look for you or if you need any further info.