You'll be giving up a good number of things to go with the Saiga over the Mini-14. Firstly, until you do the conversion (which you say you aren't going to do) the trigger on the Saiga leaves a
lot to be desired. Second, you are stuck with the expensive Saiga factory 10 round mags with no alternative options. You also lose the last round bolt hold open feature that you get with the Mini-14 as well as the Mini-14's more traditional scope mounting system. With the Saiga you're going to have to purchase a side scope mount of some sort whereas with the Mini-14 all you have to buy are rings as the scope mount on the Mini is part of the receiver. There is a very large aftermarket available for the Mini-14 and there's next to nothing out there for the .223 Saiga.
Based on your original post alone I would say don't buy the Saiga, it sounds like you would be setting yourself up for major disappointment. If you were okay with the shortcomings of the Saiga I would highly suggest purchasing it in one of the two primary AK chamberings, 5.45x39mm or 7.62x39mm.
The 5.45 would give you even cheaper ammunition than the .223/5.56 would and is pretty much the same cartridge in terms of size and performance as the 5.56 round is. In addition you would also get access to the AK74 surplus and aftermarket magazines, opening up a whole world of possibilities for outfitting your gun. You would also share parts commonality with the other AK74 variants giving you many aftermarket options for parts and accessories, plus when you got tired of shooting it as it and you converted it (which you would eventually do) it would make your conversion much simpler.
The 7.62 would cost you more for ammunition but is a much more versatile cartridge which could serve you well in any roll from plinking to self-defense all the way up to a hunting cartridge capable of taking most any game in North America. It also has even more aftermarket parts and accessories available for it than even the AK74 variants do.
It's your call and if I were you and I wasn't looking for an AK-variant gun, I would definitely hold out for the Mini-14. Don't make the mistake of buying a different gun just because it's cheaper right now, it will end up costing you more down the road when you do eventually end up buying the Mini-14 that you wanted in the first place. I'm pretty sure most everybody else on here can tell you from personal experience that if the Mini is the gun you really wanted, you will eventually buy it whether you buy the Saiga now or not.