Is there a relatively affordable way to get Doctor Who DVDs in the US?
I'm not quite sure what you're asking. With the exception of the 1996 tv-movie, which probably won't be released here due to complicated rights issues, every classic Doctor Who
story that is released in the UK is eventually available in R1 as well, usually with a lag of less than a year. Availability in retail locations can be spotty, especially lately, but Amazon.com and other online companies always sell them. The MSRP is $25 for a single-disc release, $35 for a two-disc story, and $50 for a three-disc box set, but many retailers discount them, and the MSRP also drops eventually. dvdpricesearch.com is a good place to check for releases that fit your definition of relatively cheap.
The new series boxsets are also being released here, after each season completes its run on Sci-Fi. They retail for a steep $100.