I just arrived in China with a multiple entry tourist (L) visa good for 30 days after each entry. But, I'm going to be here for almost three months.

Is there an easy and affordable way to get the visa converted to a three month visa? Or should I just plan to make a couple of border runs to Laos?

Thanks in advance for advice!

You could make the mulitple border runs but it might be cheaper (and easier) to just go to the VISA office on Beijing Lu and get a new VISA.