About Mobile Suit Gundam kits
Mobile Suit Gundam first aired on TV in 1979, according to the official Gundam site, and Bandai's model kits of it are the oldest items still on its Japanese list: the 1/144 Gundam is dated July 1980 and is listed today at ¥330 with tax, next to a 1/100 Gundam at ¥770. Bandai keeps adding new versions of the same suits, so this series has kits in almost every grade, from Entry Grade to Perfect Grade, plus Premium Bandai and Gundam Base editions.
If you want the RX-78-2 itself, the grade decides the build. The Entry Grade version (May 2021) is listed at 700 yen before tax on Bandai's English page, and Bandai's English hobby guide says some items, Entry Grade included, need no tools. The HGUC version (July 2015, 1,200 yen) is the usual first proper kit. The HG RX-78-2 [Beyond Global] of June 2020 sits between them at 2,000 yen. The RG Ver.2.0 (August 2024) and MG Ver.3.0 (August 2013) add an inner frame for builders aged 15 and over.
The old kits are getting dearer: on Bandai's January to March 2027 revision list, small-scale kits such as the 1/2400 White Base and the 1/550 Bigro go from ¥330 to ¥660 with tax. See the price changes page for the full list.