I have just finished a 126,000 word novel (set in NZ) which I am confident is a very good story and novel. In 2006 I sent my first 30,000 words to the UK Writers' Workshop where (for a fee) an editor analysed and advised on my work. Taking his advice I re-wrote the 30,000 words and in 2008 resent him (to read on a friendly "mentor" basis) 20,000 words. He praised my work saying he enjoyed it immensely, and that I was "on the right track". I say all this only to point out that I have strived to gain objective comment on my novel and so far it's all been good.
My problem now of course is to interest an agent! My question to you is this: Would it work / be acceptable to send a cheque for say $300 with my submission and say: Please read my first 60,000 words and here's something in recognition of your valuable time? I'm not wealthy but I believe an agent ought to be paid to spend say 5 hours reading my first 60,000 words and I'd be happy to pay just to get SOMEONE to read my damn book that I slaved over for five years! What say you?
What a tempting notion, to be paid to read submissions ... But it's ethically dicey and, for that reason, any agent who is conducting business properly does not accept fees to read submissions. Yes, it would make our business model more feasible, particularly in our small Antipodean market of smallish advances and less books published than elsewhere, but if I accepted a fee for reading a submission the author would (quite reasonably) expect to get a result in their favour - and I don't sign up many new clients. I don't think many authors would take kindly to sending money for an agent to read the submission only to be told that the agent isn't interested. Paying a fee creates an expectation that in most cases we can't fulfil.
An agent's existing clients pay for their time, and it's those existing clients who are, technically, paying for the submission-reading time. Except for this fact: the reading of submissions tends to happen in our private time. So, yes, we're doing it for free, but to do it for fee is not just unwise but unethical. If we choose to take on a client they need to know we're doing it because we love their work, not because they've paid us to read their submission.
In other words: don't send money. Not only won't it be accepted (unless the agency is dodgy) but it's likely it won't win you any friends.