GPS receiver which works as reference station

Hi, Im writing Bachelor thesis and my work will be based on how DGPS is working (more or less, precise is analysis of GBAS system and building a laboratory for studying how is it working, what message is sending to the aircraft and so on) and I need to buy GPS receiver which will be working as reference station as well, which is as far as I see quite a challenge. I mean Im not really deep in the subject and I don't know many places where I can find such things. So here is my request: is anybody able to tell me where I could find such device? Another thing, also quite important, would be great if it could cost below millions of euro, dollars, pounds... Thanks for your help!