Border run

Any Nha Trangers know the visa border run drill for here in Nha Trang. We are planning on staying long term. Now have a single entry 30 day. Am told the local whomever can grant two extensions. Then I guess its to the border for us. Is there a Cambodian border run nearby I can go to? Are there any travel agencies that can arrange the trip for me? Please don't say I must go to HCMC, was really wanting to avoid that.
If anyone knows of a good place for rent, we are looking (Maybe $350-$450 range).

Be aware you cannot get a Vietnamese visa at the border crossings, unless it has changed recently. You will have to travel all the way to phnom phen. A 3 month multi entry visa is relatively easy to obtain and a 6 onth multi-entry requires approval. Not sure how difficult the 6 month one is. Also, you can obtain your Cambodian visa online and it does not take up any pages in your passport.

Thanks paramyd for the good info.