My original post on Primaris Wulfen got a fair bit of attention. They are actually pretty inexpensive to do if you buy everything from ebay resellers. By far THE most expensive part of them is the actual Wulfen weapons. The key part that makes them recognizably wulfen is the heads, which are cheap from Ebay bits sellers, you can get a dozen heads for about $5. The arms are about as cheap, you can get 10 pairs for also about $5. Frost claw pairs are also cheap because they aren't the best option, but again they're cheap and easy. The axes and the thunder hammer and shields were the most expensive parts of the conversions, if you have enough sparebits or can make them then that is where you can save the most. So you're looking at $20 for the heads and bare arms if you already have 20 marine bodies and the weapons or $10 if you JUST do heads.
I originally made 15 wulfen from normal sized space marines using a mix of plastic wulfen arms and resin Spellcrow arms, plastic wulfen heads and actual wulfen axes/hammers/claws. I specifically shelled out the extra money for the actual Wulfen weapons to make sure the conversions would be acceptable to all opponents since I was using regular sized marines instead of larger 40mm based ones and they cost me about $30 per squad of 5. The Primaris conversions are about that same cost and again, I shelled out the extra money for acual Wulfen axes and hammer/shields to make them absolutely recognizably Wulfen conversions.
If you aren't fussed with using actual
GW models then by far the cheapest route, and one I've considered using for a very long time, is to use the old Confrontation Wolfen models. The plastic Wolfen actually hve a lot of really good detail, are the correct size, and well, they're giant fething werewolves already. Weapons would take some work, but you could buy a box of 3 Shadow trackers for $4, so for $28 plus shipping you'd have all 20
https://www.miniaturemarket.com/rkh-wfel07.html
And finally, yes, beastmen could work, but they'd take a fair bit of greenstuffing to make them look like wolves instead of beastmen. I used a Gor as a test some years back, turned out OKish, but was way too much effort for what I got out of it. They would take the most work, they are way too small, and at $41 for a unit of 10 they aren't even cheap
My favorite looking option is of course the Primaris conversions, with the Confrontation models very close behind. If you plan on playing against people that don't mind non-
GW models, my suggestion is the Confrontation fgures.