Custodes are a pretty cheap army tbh. I think a whole 2000 point army can cost under £300 even when bought at standard retail price, which is relatively cheap for a 40k army. Might be off by a bit, but I think you only need about 9 kits to build a 2k list. Might not be a great list, but making a great Custodes list doesn't cost much more than a mediocre one, and I don't think there's really such a thing as a bad custodes list because their roster is small and all pretty good so it's hard to mess up.
Still not cheap by any means, but some 40k armies, such as ork, tyranid or guard infantry based lists, can cost three times as much to build because their infantry cost so little. If I wanted to build a Catachan infantry list I'd be paying through the nose for it, and the sculpts for guard have aged poorly.
Orkz are actually getting a new bunch of models sometime soon, a new kit for basic boyz being part of it, but most of it being focused around the new Beast Snaggaz. Orks who eschew vehicles and shootas in favour of tekked up stabbaz, squigs and bioniks to replace the bits that get bitten off by squigs. Fighting various giant monsters in close combat has resulted in them being bigger and tougher than most orkz, though not to the extent of Nobz. They're essentially Snakebites, but fluffed so that they can fit into any klan rather than only being marketable to people who like Snakebites.
Notable models are the return of an old Snakebites character, Zodgrod Wortsnagga who has an unusual fondness for gretchin, a new gretchin mini to accompany the Beastsnagga Doc models which in order to keep up with the squig riding snaggaz has bionic legs to run super fast, the gretchin assistant meanwhile has a single wheel where it's legs were to try and keep up with.
Also one of the minis is a gretchin riding a squig with a missile stapped to it. So some variant of bomb squigs might be coming back.