It depends on what you mean by clone.
You can easily convert a Saiga to a fixed stock rifle and use Bulgarian parts for the front end and it won't be too expensive. You'll have a functional shooter, but that's not a true clone.
Clone is making the rifle as close to an AK74M as possible. That means AK74M front end parts, proper 5.5mm folding stock with PG plate, Russian black poly furniture, proper muzzle device and selector markings at a minimum, including a professional builder that knows this type of conversion. If that is what you are after it will be considerably more expensive than any fixed stock conversion, and may be just easier to by an SGL31-94 rather than put the effort into getting your 5.45 Saiga to that configuration. SGL31-84 and 31-94's are already converted to be very close to 74M rifles out of the box and are the best place to start. Unfortunately that boat has sailed and they are extremely expensive when you can find them.
As far as the SLR104 goes it is not a 74M at all and does not make a good clone, though it is a hell of a rifle and worth the price. They make great early 80's pattern rifles with laminate furniture, and can use plum furniture too. If you don't care about the modern AK74M in all it's details it will be cheaper to buy an SLR104 and call it a day than to get your Saiga to the same level.
Again, this comes down to what you mean by clone. You can put black poly furniture on an SLR104 and will basically look the same as a 74M. The devil is in the details as they say
http://russianoptics.net/AK74Overview.html for a few photos and a quick overview on the 3 main eras of AK74s
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