Basically, if you want to get into the PCE / TG16 scene be prepared to spend. You don't have to be a millionaire but it's just not like the more popular systems either. It'll depend on what you wanna play and how patience you're.
Eventually you will want to play CD games (there are some great games like Dracula X, Cotton, Star Parodier, Gate of Thunder, etc), so it is best to get a Duo system since the beginning. According to the experts, the Duo-R / RX systems are more reliable (I got me a Duo-R and it's a great system) but if you come across a cheap Duo system you can have it recapped as Wilykat pointed out.