Wow, this is a confusing thread for noobs, big time.
First to clarify some things: SCART is not a signal type, its just a form factor for the connector, SCART connectors can accommodate RGB, composite, component, s-video, RF, mono audio, stereo audio, +5V, and probably some other stuff as well from time to time. When people talk about getting RGB from a PCE it is often convenient for people in Europe to have it packaged into the SCART connector, but that's because their TVs have SCART sockets on them. American TVs don't. There is no point in going to SCART cables specifically unless you have something to plug it into.
In the US the vast majority of RGB capable displays are either inconvenient arcade monitors with no housings, or ancient 13" computer monitors from the 80s. Even then, they never have SCART sockets on them.
Secondly: if by "HDTV" you mean an LCD or plasma, you need a lot more than an RGB signal. SD game systems look like SHIT on these displays no matter what signal type you are using. A box like an XRGB, Edge, or other things is pretty much required unless you are blind or under the age of 20 (thereby, often times, not actually knowing what a good SD signal even looks like). You can convert the RGB to component, but it still going to be shit and quite possibly laggy.
So, figure $300 on this upgrade, if not more.