Hi Ave!
Such a plugin does not exist in LOTRO, for the simple reason that a plugin is unable to access information from the AH. You'll have to read guides and use common sense, I'm afraid.
Some tips: ALL crafting materials are worth saving and selling! So really simply put: any item with a light green background (like
this one for instance) should be saved, preferably stockpiled and either used or sold. Don't vendor them! There are ALWAYS people looking to buy them - use the Trade channel or the GlobalLFF (or GLFF) channel to find them. For some reason, the lower tier materials actually often sell for pretty serious coin! I guess people are just lazy. So-called "crit items", which are items a crafter needs to create a "crit" version of a craftable item (simply a better version than the standard one) are also often in high demand, though this varies depending on craft and also just on availability. Do some reading, find out what sells well and what doesn't - it's not too hard to learn.
Once you get a bit of a feel for what 'normal' prices are, you'll be able to use the AH more and more as a means of earning cash. Browse the AH late at night or early morning and buy up whatever is selling cheaply, then put it back for a (slightly) higher price. You'll take some hits here and there but if you play your cards right, this can net you a sizable income.
Last, but not least: Farming! And I mean the craft, not the grind. Create a farmer character, level him up (which is very easy) and get all the recipes from the Expert Farmhand. Required materials to do farming are ALL cheap and ALL sold by the Farmhand. Make stacks of items, then put them on AH for a reasonable price. Don't put 10 stacks on at once, ofc, but a few every day keeps the money steadily flowing in
Hope this helps a bit, feel free to PM me if you need more specific advice on certain things
