Converting 4u Server To 2u

I just built a low end server using a 4u chassis I had at home. Before bringing it to the colo facility, I was wondering if I would be better to put the hardware in a 2u chassis instead to save money on the long run.

I am considering the 2u SC826 SuperMicro chassis. I am used to buy my parts from the local shop. I can fix my current 4u server since it does not contain 'proprietary' parts such as backplanes that are built for a specific server.

I could save about 55$ per month by colocating a 2u instead of a 4u server. The chassis is about 700-800$.

I was wondering how easy it is to replace a proprietary part such as a backplane if my server breaks in 3 to 4 years? Will I be left with an unusable chassis if I cannot find the part? Is it worth it to have a 2u chassis vs 4u when I can fit any standard component in the 4u while I need more expensive and hard to find parts for the 2u? How many years can I expect to be able to find replacement parts for proprietary hardware such as backplanes in such a 2u chassis?