I need to get wifi to an outbuilding 200 feet away from my rbr50 router.

200ft to a metal skinned building. There are only two reasonable solutions:

• A physical ethernet cable (max 328ft.) which as you have discovered can be difficult to install. (and costly if you pay someone to do it).
• An ethernet bridge, which appears to the devices on each end as an ethernet cable.
  Search for "WiFi bridge" on Amazon.  Products range from the $40 TP-Link N300 to several hundred dollars.
  https://www.amazon.com/TP-Link-CPE210-300Mbps-dual-polarized-directional/dp/B00P4JKQGK/ref=sxin_9?ascsubtag=amzn1.osa.33759645-a1e0-489a-b594-fb9c53756c52.ATVPDKIKX0DER.en_US&creativeASIN=B00P4JKQGK&cv_ct_cx=wifi+bridge&cv_ct_id=amzn1.osa.33759645-a1e0-489a-b594-fb9c53756c52.ATVPDKIKX0DER.en_US&cv_ct_pg=search&cv_ct_we=asin&cv_ct_wn=osp-single-source-gl-ranking&dchild=1&keywords=wifi+bridge&linkCode=oas&pd_rd_i=B00P4JKQGK&pd_rd_r=14c1613b-c4ba-4ed5-b995-cb8063891edb&pd_rd_w=bIHgl&pd_rd_wg=sd69b&pf_rd_p=9d7390bd-9235-4046-b950-0331f14c437d&pf_rd_r=SA1V7PVH0B26DNNVZ2V2&qid=1609647097&sr=1-1-d9dc7690-f7e1-44eb-ad06-aebbef559a37&tag=pcmagcontent-20 
  People have reported success with a variety of brands.  I'm just horribly conservative, but my preference is to look for "established companies" such as TP-Linl, D-Link, Netgear, or Ubiquiti.  At least with several hundred product reviews.
• The unit on the "house end" probably can be installed indoors and will penetrate an ordinate house wall easily.  The unit on the far end may need to be mounted outside that metal shell.