Warning, it's an addictive hobby...
I would suggest that you start with a good ROF sporter with matching bolt, barrel and receiver. Make sure the bore rates very good. These can still be found at gun shows for around $100. Personally, I avoid Australian (Lithgow) sporters only because correct parts are more difficult to find. The parts you will need will for a full ROF No1 MkIII resto will run you roughly $300 to $400 depending on what you need and how fussy you are. I buy most metal bits like barrel bands and screws off of eBay. Upper hand guards (the long one) are getting very difficult to find. However very good repros come up for sale on this site from time to time, as well as other misc parts. Your biggest challenge will likely be finding a decent stock forearm. Expect to pay at least $150 for one in very good condition. Note that some are walnut and some are beechwood, and it can be difficult to distinguish between the two in photographs. My preference is walnut. I've restored numerous No1 MkIII's but there are guys on here with more experience at it than me. Liberty Tree Collectors is a good source for Enfield parts too, but these days most of their stock seems to be well worn and DP marked. Good luck!