Remember that you can buy your RP as high as (ST + HT) very cheaply. Do that. Once your RP are at 20+, you recover 2 per day instead of 1
and it takes twice as much radiation to really hurt you. Very Rapid Healing also helps your recovery (of both RP and HP!); it's been a popular choice in our group.
Ironically, if your game includes mutations, there are some useful ones for avoiding rad damage. Natural Anti-Rad (ATE1, p. 27) lets you exceed the ST+HT cap on your RP by as much as +20! In theory, you could start the game with RP 40+ and Very Rapid Healing, which means it takes about 4x as much radiation to hurt you
and you heal it 8x as fast! If you have
Pyramid #3/90: After the End, check out the Geiger Counter mutation on p. 11; it is, without a doubt, the best way to identify and avoid irradiated areas. (All-Sight on p. 10 is the second best, as it gives you a Vision roll to spot gamma radiation.) Also see the notes in that article for Boosted Hemoglobin and Environmental Filter (both p. 7).
Finally, gear like the advanced biohazard suit (ATE2, p. 47) offers PF against radiation. But even with the Cheap modifier (i.e., DR 0), it's still a $6,400 value, so you probably can't start with it. The same with chelating agents (ATE1, p. 30), which are safe but freakin' expensive. The best option as far as gear goes may be SieverTasty (ATE1, p. 30), which is effective but has some nasty drawbacks.