Another advantage of the single axle utility-type trailer is that you can get it back on some pretty gnarly primitive roads that you could never negotiate with a horse trailer (I've done it). If it is all you can afford or have access to, it is excellent way to start with a couple of llamas. If you move up to a horse trailer, you can still use the utility trailer for all kinds of other hauling work.
I would be warry of a single axel trailer. Think of being on the interstate in the summer, having a blow out and having to jack the trailer up on 100degree asphault while you animal cooks. And jacking up all that shifting wobbly weight.
A used two horse trailer can be found for just above $2,000. Redo the bearings for $150 and $500 in 10 ply tires and you ready for about any road.
Buy nice, not twice.