However, you can just make a screenshot of the cells and mail the sceenshot. If you MUST send PDF's, several third-party PDF apps allow for importing images (including screenshots) and exporting / mailing a PDF created out of those images. (Let me know if you need such a list and I quickly compile one.)
Or, if you don't need PDF, copy the page to a brand new Excel document and send it as a native Excel page.
First, do you have Apple's own “Numbers”? It's not only able to export / mail PDF files from inside the app (unfortunately, there's no “Send to” inside – this has always been a problem), but also do it textually – as opposed to just making a screenshot of the current screen and making a PDF of it by accessing the screenshot in the Camera Roll in a PNG->PDF-conversion capable PDF reader.
If you still want to go the second way, I've tested most of the PDF / generic docs readers I have.
The ones supporting image → PDF conversion are as follows:
PDF Reader Pro (Yuyao; $6; http://itunes.apple.com/us/app/pdf-reader-pro/id300298606?mt=8 ) (can convert single images only!)
PDF Reader (Kdan Mobile Software; http://www.kdanmobile.com/en/pdf-reader/ ; http://itunes.apple.com/us/app/pdf-reader-ipad-edition/id367816156?mt=8 ; $5) (several in one! Just follow the built-in help at “i” icon at the bottom left > select PDF Scanner)
PDF Reader Pro (iTech; http://itunes.apple.com/us/app/pdf-reader-pro-edition-for/id364502063?mt=8 ; $10) (multiple; tap the “Scan” icon at the bottom center, tap the film cartridge icon in the bottom left; tap all images you want to import; when you're finished, tap “Make PDF” (second icon on the bottom left)
Readers that can't:
GoodReader (for iPad)
QuickOffice Pro HD
iPDFReader by Tatvasoft
iRead PDF (Aji)
Crashes under iOS 5.1.1: