In general, I've found that to buy cheap rope turns out to cost me more in the long term, so I try to buy good rope and look around for the deals. That is, try to buy wholesale, to buy a full reel of 100 metres (you'll use it all eventually), and so on.
For halyards, there's no question that only the best is good enough. It works harder than the other lines in a junk rig, and you will go aloft on it from time to time. My main halyard is 10mm Marlow, braid cover over a slow 3-strand core. It is lasting extremely well. My mizzen halyard is 10mm treble braid (yes, treble braid) from a Spanish maker whose name I've forgotten. It is lasting extremely well. I wish I could get more of it, because it cost no more than double braid, and is much better rope.
For sheets, lower grade rope is good enough - as long as the sheet is to be hand-hauled only. 10mm dinghy sheet rope costs less than double braid, and will do the job. However, if a winch is used, standard yacht-quality double braid becomes advisable.
For the lifts, and the yard parrel, which both work quite hard, good double braid is advisable.
For running luff parrels, and batten parrels, the demands are lower, and lower grade rope is OK.
I try to get black or dark-coloured rope, for the same reason as I use black sail thread - longer life under UV exposure.
I find the PJR rope sizes to be on the small side. I wouldn't want a heavily-loaded, hand-hauled line (halyard, yard parrel or mainsheet) to be less than 10mm. My mizzen sheet is 8mm, and is OK, because the loads are light.
Many braided ropes are difficult or impossible to splice. I've given up trying. I use what my "Encyclopaedia of knots and ropework" calls a "scaffold hitch". It is a semi-permanent knot that works on slippery, hard rope as well as more amenable rope. It can be made with a very short tail, and I have never known it to slip, once settled down. I use it on all running rigging. I've put some pictures into my photo albums.