Well, your second question is probably the easiest to answer. I imagine that the price is the same as in the
Player's Handbook (p.222), i.e. 5sp for a typical room and 2gp for a luxury room.
The first one is tougher. The
Eberron Player's Guide (p.13) tells us that the lower class (of which I guess a guard belongs to) has no more than a handful of silver pieces on himself at any one time. Casting the net a bit wider, the 3.5 DMG(p.105) tells us that a laborer can earn 1sp per day, while a mercenary can earn 2sp per day. Seems likely that an ordinary guard might earn 1sp per day, while a better trained and more trusted one might earn 2sp per day.
I could have sworn that bribes were mentioned under skills somewhere in 3.5 or 4th ed, but I'll be darned if I can find the mention. However, you might try to figure it out from the above. If a guard earn 1sp/day or 3gp per month, then 3gp is a months salary, and more than he has in his pocket. 40gp is more money than he will see in a year. Whether any of those are a good bribe depends on what you want him to do, and how loyal he is to his employer.
By the way, if you follow the 3.5 DMG, then a skilled craftsperson or scribe would earn approximately 3 times as much (9gp/month), while an architect, alchemist, barrister or low-rank officer would earn somewhere between 5 and 10 times as much(15-30gp/month). These guys probably form the the lower parts of the middle class mentioned in the
Eberron Player's Guide.