The variety of available trailers is as wide as you can imagine. From  single axle on small wheels steel trailers, to trailers with hard plastic covers to luxury drive-in, kneeling trailers made of lightweight alloys equipped with remote control electric winches, its own lighting and so on. There is a trailer for every pocket. 

Low budget solution is a used trailer which can be acquired for  as little as 500 Euro. There are however crucial considerations to be taken into account. Each trailer has a determined gross vehicle weight rating (GVWR) which also determines what is the maximum weight of the car you can transport on the trailer.

What is more, each car has a predetermined gross maximum weight of the trailer it can haul. With normal passenger car driver license the the gross maximum weight of the car + trailer combination is 3,5 tonnes. Note: the 3,5 tonnes it is not the actual weight, but theoretical gross maximum weight. So, before deciding what trailer to buy make sure your car can haul it, your rally car can be transported on the trailer and you have the driver's license that allows you to operate such car-trailer combination. Mistake in understanding these complicated set of limitations before buying the the trailer can be very costly ! 

Otherwise the only limit  is your budget  !