Minas Gerais is nice all year round and it never gets as hot and humid as Rio. However it can get cold at nights and it can rain. Be warned that average temperatures are only that. You are up in the hills on this trip and it can get very very cold in winter.
Like in Paraty there are cultural and religious festivals throughout the year in both Tiradentes and Ouro Preto, and prices in pousadas rise at these times
Price Guide
Prices below are low season rates for two people in brazilian reais (R$). Standard double room, with en-suite shower room, breakfast included.
$
R$ 80 - 140
$ 40 - 70 € 33 - 58 £ 24 - 43
$$
R$ 141 - 220
$ 70 - 110 € 58 - 91 £ 43 - 68
$$$
R$ 221 - 360
$ 110 - 180 € 92 - 150 £ 68 - 111
$$$$
R$ 361 - 500
$ 180 - 250 € 150 - 208 £ 112 - 155
$$$$$
R$ 501 - 1000
$ 250 - 500 € 208 - 416 £ 155 - 310