Any good 'horse' quality grass hay(no mold, no noxious weeds, not too dusty) is usually fine to feed to rabbits. Timothy is just a common one to feed, especially here in the US. But orchard, meadow, oat(without too many seed heads), etc, are usually all fine to feed, provided a rabbit isn't sensitive to a particular hay and the hay has the right balance of necessary components for good weight maintenance, gut motility, and tooth wear(explained in detail below).
Lucerne/alfalfa is different. It's not a grass hay but a legume hay, which is high in calcium and protein and not advisable to feed to adult pet rabbits, but is usually fine as a supplemental hay(in addition to a grass hay) for growing rabbits and nursing does. For adult pet rabbits, the excess calcium in it can sometimes cause bladder/kidney issues for some rabbits, and the excess protein may cause obesity, excess cecotrope production, and smelly urine(increased ammonia smell).
The meadow and lucerne hay may be cheaper because it doesn't have to be imported, because of being more difficult to grow in an area, and/or because it's less available as a crop than another hay. Like around my area, lucerne/alfalfa, fescue, and orchard are easier hays to grow, where as timothy has to be grown in slightly cooler climates, so can be a bit more expensive than the other hays as it has to be trucked in from up north.
As for your rabbits preferring the timothy over the meadow, that just has to do with the taste of the particular grass being fed, as well as the batch(crop) of hay being fed. Certain grasses taste different from each other, but even different batches(crops) of timothy(or other grasses/hay) can differ in taste. You could be feeding one batch that your rabbits love, then a new batch(crop) of the same grass type comes in and you could find your rabbits not liking it as much. It's all about the growing conditions, the drying conditions, and when a particular hay is cut and baled.
Some other considerations of grass hay choice that don't have to do with the taste, are the coarseness of the hay(growth and maturity of when the hay is cut) and the silica content of a particular grass. Usually the best cut of hay is a medium coarse hay that is a mix of mostly leafy strands, but with some coarse stems as well. The leafy strands provide the needed protein and nutrients for good health and weight maintenance, and the stems provide the indigestible fiber that is needed for good gut motility. A really leafy hay with no hard stems, can sometimes be too rich of a hay, which could result in weight gain and/or excess cecotrope production, but also slower gut motility because there is less indigestible fiber in it. And a cut of hay that is too coarse with mostly hard stems, can be too devoid of nutrients that could result in health issues like weight loss, impacted cecum, and fur chewing(protein deficiency).
The silica content in particular grass growth is important because that's what affects proper tooth wear the most. Silica is abrasive, so causes tooth wear as a rabbit chews the plant. The more silica, the more tooth wear occurs. But too much is also not good, as plants really high in silica, rabbits won't eat those plants. But for the general grass hays that would be fed to rabbits, you don't have to worry about excess silica, just enough for good tooth wear. Around here, orchard grass is one of the higher silica content grass hays.
silica in hay and how it applies to rabbits
It's all about finding the right balance with your hay, and feeding one that your rabbits eat well. If your rabbits eat the meadow hay fine, their poops still stay a healthy size and consistency, and you feel the hay is abrasive enough that it will be good on tooth wear, then the meadow should be fine to feed as well. If you don't feel it's abrasive enough, if it's not the right mix of leaf and stem, and/or your rabbits don't eat it very well that it affects their fecal poop size and consistency, then it's probably best to stick with the timothy hay.
https://wabbitwiki.com/wiki/Hay
