I can tell you my first hand expierence, as i've started a BP about a month ago.
I was playing single box only, and donated 2 euro to get top D magic blunt and D bow for RBs. So, starting from 20 to ~45 you are welcome in any RB party as long as you have bow, no one cares about your prof.
You can also try soloing undeads with undead smite - I did for some time, very low efficiency since you burn your mana in 3-5 minutes and then regen it for up to 10 minutes. Keep in mind I've donated for top D 2h blunt (atuba), without donations it gets even worse, the only pros is that by farming undead you actually get adena, while RB are usually not profitable unless you are lucky and get some weapon drop.
So, I got my 40, completed my second prof and became a noble healing class - Bishop. And thing started to change really quick. First of all no one at all need BP on farming parties, since he adds nothing to that party in terms of xp/time ratio. Well we have low lvl acum and bers, but every dude on the server has boxed PP, no one needs even those. You are not needed as healer on RB either, since summoners have infinite mana and we burn our mana in like 5 minutes. And also ppl stop taking you to RBs from ~45 since they want real DDs. Well if you donate for +10 emi, i guess you will get a spot, otherwise very unlikely.
I've met a couple guys that actualyl took me to farming, once... Guess they realised how useless BP is, but were nice enough not to kick me right away, though did not ever invite after that, still have them in friend list I was looking for CP, i had a chat with a guy called Fortuna, had him in my friend list to "watch my progress", but they need 70+ bishops and they did not help me in anyway (dont blame them, it is risk to help unknown player), so you will be on your own for a looooong time.
So I've been struggling to get lvl 47 by solo grinding mobs (no one was accepting me on RB/farm party) with our smite undead nuke, which is just terrible in terms of power-to-mana ratio, real mages hit x1,5 harder for x1.5 less mana and any target. The new 2nd prof nuke... dont even waste SP on it. It can be used on any target, but it has even worse (hard to imagine) power-to-mana ration and it has 4s cooldown which makes it completely useless.
Aaaaand at lvl 47 I've decided to reroll into TK (that was about week ago). I am lvl 53 TK atm, it took me about 4 days to get TK to same level as BP, and I am always wanted in RB parties, aoe parties, already got good clan.
So , to sum it up. Unless you have tons of best gear, you have a CP that will assist and help you leveling up - do not start as BP.
P.S.
Yep, at 70+ i bet they are