I have not been in touch with market except I know price..
Change interval depends upon engine condition... But engine itself tells when it's not liking oil anymore (sound), one indicator is colour, full black is deadend, change at dark brown.
and if engine is very old in operation, I suggest to use sludge cleaner before removing old oil and using new. it has been discussed before by me and several other PWMs.
5W-50 (only Mobil-1) Price N/A but u have, Interval: Should be 12K min
5W-40 (ENOC, ZIC, Shell) Price N/A, Interval: Should be 10K min
5W-30 (Caltex, ENOC & ZIC has 0W-30) Price, 2500,2290,2600, Interval: 8K max
(I used ENOC one and had to change after 5K because it really cleaned engine, there is also one warning that it may happen that full syn oil removes waxes and that stucks in your oil filter and choke it, better use sludge cleaner before)
10W-40 (Mobil, Castrol Magnatec, ENOC, ZICA, Shell) semi-syhth. Price: ~2700 old, 2300,2000,?,2260, Interval: 6K max