Gists de tentativa de consumo da API passando o objeto Posto para o método.

Price.java

AsyncHttpClient client = new AsyncHttpClient();

            RequestParams params = new RequestParams();
            params.put("valor_etanol", this.valorEtanol);
            params.put("valor_gasolina", this.valorGasolina);
            params.put("valor_diesel", this.valorDiesel);
            params.put("posto", "COMO INSERIR AQUI O OBJETO POSTO?");
            client.addHeader("Authorization", String.format("Token %s", token));
            client.post(uri, params, new AsyncHttpResponseHandler() {
                @Override
                public void onSuccess(int statusCode, Header[] headers, byte[] responseBody) {
                    Log.e("Price", String.valueOf(statusCode));
                    resultadoInsertPrice = true;
                }

                @Override
                public void onFailure(int statusCode, Header[] headers,
                                      byte[] responseBody, Throwable error) {
                    Log.e("Price", String.valueOf(headers));
                    resultadoInsertPrice = false;
                }

            });